Hi Greg, hi Sasha,
Please consider to include following fixes in to stable tree. The 6 patches from Ming was fixing a deadlock, they are included around kernel 5.3/4. Would be good to included in 4.19, we hit it during testing, with the fix we no longer hit the deadlock.
The md fixes is for a panic regarding handle flush.
the last one is simple NULL pointer deref fix.
Thanks! Jack Wang @ IONOS Cloud.
Ming Lei (6): block: don't hold q->sysfs_lock in elevator_init_mq blk-mq: don't hold q->sysfs_lock in blk_mq_map_swqueue block: add helper for checking if queue is registered block: split .sysfs_lock into two locks block: fix race between switching elevator and removing queues block: don't release queue's sysfs lock during switching elevator
Xiao Ni (1): md: Set prev_flush_start and flush_bio in an atomic way
zhengbin (1): block: fix NULL pointer dereference in register_disk
block/blk-core.c | 1 + block/blk-mq-sysfs.c | 12 +++++------ block/blk-mq.c | 7 ------ block/blk-sysfs.c | 49 +++++++++++++++++++++++++++--------------- block/blk-wbt.c | 2 +- block/blk.h | 2 +- block/elevator.c | 44 +++++++++++++++++++++---------------- block/genhd.c | 10 +++++---- drivers/md/md.c | 2 ++ include/linux/blkdev.h | 2 ++ 10 files changed, 76 insertions(+), 55 deletions(-)
From: zhengbin zhengbin13@huawei.com
If __device_add_disk-->bdi_register_owner-->bdi_register--> bdi_register_va-->device_create_vargs fails, bdi->dev is still NULL, __device_add_disk-->register_disk will visit bdi->dev->kobj. This patch fixes that.
Signed-off-by: zhengbin zhengbin13@huawei.com Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit 4d7c1d3fd7c7eda7dea351f071945e843a46c145) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/genhd.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/block/genhd.c b/block/genhd.c index 2b536ab570ac..6965dde96373 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -652,10 +652,12 @@ static void register_disk(struct device *parent, struct gendisk *disk) kobject_uevent(&part_to_dev(part)->kobj, KOBJ_ADD); disk_part_iter_exit(&piter);
- err = sysfs_create_link(&ddev->kobj, - &disk->queue->backing_dev_info->dev->kobj, - "bdi"); - WARN_ON(err); + if (disk->queue->backing_dev_info->dev) { + err = sysfs_create_link(&ddev->kobj, + &disk->queue->backing_dev_info->dev->kobj, + "bdi"); + WARN_ON(err); + } }
/**
From: Ming Lei ming.lei@redhat.com
The original comment says:
q->sysfs_lock must be held to provide mutual exclusion between elevator_switch() and here.
Which is simply wrong. elevator_init_mq() is only called from blk_mq_init_allocated_queue, which is always called before the request queue is registered via blk_register_queue(), for dm-rq or normal rq based driver. However, queue's kobject is only exposed and added to sysfs in blk_register_queue(). So there isn't such race between elevator_switch() and elevator_init_mq().
So avoid to hold q->sysfs_lock in elevator_init_mq().
Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Mike Snitzer snitzer@redhat.com Cc: Bart Van Assche bvanassche@acm.org Cc: Damien Le Moal damien.lemoal@wdc.com Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit c48dac137a62a5d6fa1ef3fa445cbd9c43655a76) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/elevator.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/block/elevator.c b/block/elevator.c index fae58b2f906f..ddbcd36616a8 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -980,23 +980,19 @@ int elevator_init_mq(struct request_queue *q) if (q->nr_hw_queues != 1) return 0;
- /* - * q->sysfs_lock must be held to provide mutual exclusion between - * elevator_switch() and here. - */ - mutex_lock(&q->sysfs_lock); + WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)); + if (unlikely(q->elevator)) - goto out_unlock; + goto out;
e = elevator_get(q, "mq-deadline", false); if (!e) - goto out_unlock; + goto out;
err = blk_mq_init_sched(q, e); if (err) elevator_put(e); -out_unlock: - mutex_unlock(&q->sysfs_lock); +out: return err; }
From: Ming Lei ming.lei@redhat.com
blk_mq_map_swqueue() is called from blk_mq_init_allocated_queue() and blk_mq_update_nr_hw_queues(). For the former caller, the kobject isn't exposed to userspace yet. For the latter caller, hctx sysfs entries and debugfs are un-registered before updating nr_hw_queues.
On the other hand, commit 2f8f1336a48b ("blk-mq: always free hctx after request queue is freed") moves freeing hctx into queue's release handler, so there won't be race with queue release path too.
So don't hold q->sysfs_lock in blk_mq_map_swqueue().
Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Mike Snitzer snitzer@redhat.com Cc: Bart Van Assche bvanassche@acm.org Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit c6ba933358f0d7a6a042b894dba20cc70396a6d3) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/blk-mq.c | 7 ------- 1 file changed, 7 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 0df43515ff94..195526b93895 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2324,11 +2324,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) struct blk_mq_ctx *ctx; struct blk_mq_tag_set *set = q->tag_set;
- /* - * Avoid others reading imcomplete hctx->cpumask through sysfs - */ - mutex_lock(&q->sysfs_lock); - queue_for_each_hw_ctx(q, hctx, i) { cpumask_clear(hctx->cpumask); hctx->nr_ctx = 0; @@ -2362,8 +2357,6 @@ static void blk_mq_map_swqueue(struct request_queue *q) hctx->ctxs[hctx->nr_ctx++] = ctx; }
- mutex_unlock(&q->sysfs_lock); - queue_for_each_hw_ctx(q, hctx, i) { /* * If no software queues are mapped to this hardware queue,
From: Ming Lei ming.lei@redhat.com
There are 4 users which check if queue is registered, so add one helper to check it.
Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Mike Snitzer snitzer@redhat.com Cc: Bart Van Assche bvanassche@acm.org Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit 58c898ba370e68d39470cd0d932b524682c1f9be) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/blk-sysfs.c | 4 ++-- block/blk-wbt.c | 2 +- block/elevator.c | 2 +- include/linux/blkdev.h | 1 + 4 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 8286640d4d66..0a7636d24563 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -896,7 +896,7 @@ int blk_register_queue(struct gendisk *disk) if (WARN_ON(!q)) return -ENXIO;
- WARN_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags), + WARN_ONCE(blk_queue_registered(q), "%s is registering an already registered queue\n", kobject_name(&dev->kobj)); queue_flag_set_unlocked(QUEUE_FLAG_REGISTERED, q); @@ -973,7 +973,7 @@ void blk_unregister_queue(struct gendisk *disk) return;
/* Return early if disk->queue was never registered. */ - if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)) + if (!blk_queue_registered(q)) return;
/* diff --git a/block/blk-wbt.c b/block/blk-wbt.c index f1de8ba483a9..50f2abfa1a60 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -708,7 +708,7 @@ void wbt_enable_default(struct request_queue *q) return;
/* Queue not registered? Maybe shutting down... */ - if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)) + if (!blk_queue_registered(q)) return;
if ((q->mq_ops && IS_ENABLED(CONFIG_BLK_WBT_MQ)) || diff --git a/block/elevator.c b/block/elevator.c index ddbcd36616a8..9bffe4558929 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -1083,7 +1083,7 @@ static int __elevator_change(struct request_queue *q, const char *name) struct elevator_type *e;
/* Make sure queue is not in the middle of being removed */ - if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)) + if (!blk_queue_registered(q)) return -ENOENT;
/* diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 745b2d0dcf78..3a2b34c2c82b 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -743,6 +743,7 @@ bool blk_queue_flag_test_and_clear(unsigned int flag, struct request_queue *q); #define blk_queue_quiesced(q) test_bit(QUEUE_FLAG_QUIESCED, &(q)->queue_flags) #define blk_queue_pm_only(q) atomic_read(&(q)->pm_only) #define blk_queue_fua(q) test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags) +#define blk_queue_registered(q) test_bit(QUEUE_FLAG_REGISTERED, &(q)->queue_flags)
extern void blk_set_pm_only(struct request_queue *q); extern void blk_clear_pm_only(struct request_queue *q);
From: Ming Lei ming.lei@redhat.com
The kernfs built-in lock of 'kn->count' is held in sysfs .show/.store path. Meantime, inside block's .show/.store callback, q->sysfs_lock is required.
However, when mq & iosched kobjects are removed via blk_mq_unregister_dev() & elv_unregister_queue(), q->sysfs_lock is held too. This way causes AB-BA lock because the kernfs built-in lock of 'kn-count' is required inside kobject_del() too, see the lockdep warning[1].
On the other hand, it isn't necessary to acquire q->sysfs_lock for both blk_mq_unregister_dev() & elv_unregister_queue() because clearing REGISTERED flag prevents storing to 'queue/scheduler' from being happened. Also sysfs write(store) is exclusive, so no necessary to hold the lock for elv_unregister_queue() when it is called in switching elevator path.
So split .sysfs_lock into two: one is still named as .sysfs_lock for covering sync .store, the other one is named as .sysfs_dir_lock for covering kobjects and related status change.
sysfs itself can handle the race between add/remove kobjects and showing/storing attributes under kobjects. For switching scheduler via storing to 'queue/scheduler', we use the queue flag of QUEUE_FLAG_REGISTERED with .sysfs_lock for avoiding the race, then we can avoid to hold .sysfs_lock during removing/adding kobjects.
[1] lockdep warning ====================================================== WARNING: possible circular locking dependency detected 5.3.0-rc3-00044-g73277fc75ea0 #1380 Not tainted ------------------------------------------------------ rmmod/777 is trying to acquire lock: 00000000ac50e981 (kn->count#202){++++}, at: kernfs_remove_by_name_ns+0x59/0x72
but task is already holding lock: 00000000fb16ae21 (&q->sysfs_lock){+.+.}, at: blk_unregister_queue+0x78/0x10b
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&q->sysfs_lock){+.+.}: __lock_acquire+0x95f/0xa2f lock_acquire+0x1b4/0x1e8 __mutex_lock+0x14a/0xa9b blk_mq_hw_sysfs_show+0x63/0xb6 sysfs_kf_seq_show+0x11f/0x196 seq_read+0x2cd/0x5f2 vfs_read+0xc7/0x18c ksys_read+0xc4/0x13e do_syscall_64+0xa7/0x295 entry_SYSCALL_64_after_hwframe+0x49/0xbe
-> #0 (kn->count#202){++++}: check_prev_add+0x5d2/0xc45 validate_chain+0xed3/0xf94 __lock_acquire+0x95f/0xa2f lock_acquire+0x1b4/0x1e8 __kernfs_remove+0x237/0x40b kernfs_remove_by_name_ns+0x59/0x72 remove_files+0x61/0x96 sysfs_remove_group+0x81/0xa4 sysfs_remove_groups+0x3b/0x44 kobject_del+0x44/0x94 blk_mq_unregister_dev+0x83/0xdd blk_unregister_queue+0xa0/0x10b del_gendisk+0x259/0x3fa null_del_dev+0x8b/0x1c3 [null_blk] null_exit+0x5c/0x95 [null_blk] __se_sys_delete_module+0x204/0x337 do_syscall_64+0xa7/0x295 entry_SYSCALL_64_after_hwframe+0x49/0xbe
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&q->sysfs_lock); lock(kn->count#202); lock(&q->sysfs_lock); lock(kn->count#202);
*** DEADLOCK ***
2 locks held by rmmod/777: #0: 00000000e69bd9de (&lock){+.+.}, at: null_exit+0x2e/0x95 [null_blk] #1: 00000000fb16ae21 (&q->sysfs_lock){+.+.}, at: blk_unregister_queue+0x78/0x10b
stack backtrace: CPU: 0 PID: 777 Comm: rmmod Not tainted 5.3.0-rc3-00044-g73277fc75ea0 #1380 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS ?-20180724_192412-buildhw-07.phx4 Call Trace: dump_stack+0x9a/0xe6 check_noncircular+0x207/0x251 ? print_circular_bug+0x32a/0x32a ? find_usage_backwards+0x84/0xb0 check_prev_add+0x5d2/0xc45 validate_chain+0xed3/0xf94 ? check_prev_add+0xc45/0xc45 ? mark_lock+0x11b/0x804 ? check_usage_forwards+0x1ca/0x1ca __lock_acquire+0x95f/0xa2f lock_acquire+0x1b4/0x1e8 ? kernfs_remove_by_name_ns+0x59/0x72 __kernfs_remove+0x237/0x40b ? kernfs_remove_by_name_ns+0x59/0x72 ? kernfs_next_descendant_post+0x7d/0x7d ? strlen+0x10/0x23 ? strcmp+0x22/0x44 kernfs_remove_by_name_ns+0x59/0x72 remove_files+0x61/0x96 sysfs_remove_group+0x81/0xa4 sysfs_remove_groups+0x3b/0x44 kobject_del+0x44/0x94 blk_mq_unregister_dev+0x83/0xdd blk_unregister_queue+0xa0/0x10b del_gendisk+0x259/0x3fa ? disk_events_poll_msecs_store+0x12b/0x12b ? check_flags+0x1ea/0x204 ? mark_held_locks+0x1f/0x7a null_del_dev+0x8b/0x1c3 [null_blk] null_exit+0x5c/0x95 [null_blk] __se_sys_delete_module+0x204/0x337 ? free_module+0x39f/0x39f ? blkcg_maybe_throttle_current+0x8a/0x718 ? rwlock_bug+0x62/0x62 ? __blkcg_punt_bio_submit+0xd0/0xd0 ? trace_hardirqs_on_thunk+0x1a/0x20 ? mark_held_locks+0x1f/0x7a ? do_syscall_64+0x4c/0x295 do_syscall_64+0xa7/0x295 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x7fb696cdbe6b Code: 73 01 c3 48 8b 0d 1d 20 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 008 RSP: 002b:00007ffec9588788 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0 RAX: ffffffffffffffda RBX: 0000559e589137c0 RCX: 00007fb696cdbe6b RDX: 000000000000000a RSI: 0000000000000800 RDI: 0000559e58913828 RBP: 0000000000000000 R08: 00007ffec9587701 R09: 0000000000000000 R10: 00007fb696d4eae0 R11: 0000000000000206 R12: 00007ffec95889b0 R13: 00007ffec95896b3 R14: 0000559e58913260 R15: 0000559e589137c0
Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Mike Snitzer snitzer@redhat.com Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk (jwang:cherry picked from commit cecf5d87ff2035127bb5a9ee054d0023a4a7cad3, adjust ctx for 4,19) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/blk-core.c | 1 + block/blk-mq-sysfs.c | 12 ++++----- block/blk-sysfs.c | 44 +++++++++++++++++++------------ block/blk.h | 2 +- block/elevator.c | 59 +++++++++++++++++++++++++++++++++++------- include/linux/blkdev.h | 1 + 6 files changed, 86 insertions(+), 33 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c index ce3710404544..80f3e729fdd4 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1059,6 +1059,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id, mutex_init(&q->blk_trace_mutex); #endif mutex_init(&q->sysfs_lock); + mutex_init(&q->sysfs_dir_lock); spin_lock_init(&q->__queue_lock);
if (!q->mq_ops) diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index 5006a0d00990..5e4b7ed1e897 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -264,7 +264,7 @@ void blk_mq_unregister_dev(struct device *dev, struct request_queue *q) struct blk_mq_hw_ctx *hctx; int i;
- lockdep_assert_held(&q->sysfs_lock); + lockdep_assert_held(&q->sysfs_dir_lock);
queue_for_each_hw_ctx(q, hctx, i) blk_mq_unregister_hctx(hctx); @@ -312,7 +312,7 @@ int __blk_mq_register_dev(struct device *dev, struct request_queue *q) int ret, i;
WARN_ON_ONCE(!q->kobj.parent); - lockdep_assert_held(&q->sysfs_lock); + lockdep_assert_held(&q->sysfs_dir_lock);
ret = kobject_add(&q->mq_kobj, kobject_get(&dev->kobj), "%s", "mq"); if (ret < 0) @@ -358,7 +358,7 @@ void blk_mq_sysfs_unregister(struct request_queue *q) struct blk_mq_hw_ctx *hctx; int i;
- mutex_lock(&q->sysfs_lock); + mutex_lock(&q->sysfs_dir_lock); if (!q->mq_sysfs_init_done) goto unlock;
@@ -366,7 +366,7 @@ void blk_mq_sysfs_unregister(struct request_queue *q) blk_mq_unregister_hctx(hctx);
unlock: - mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->sysfs_dir_lock); }
int blk_mq_sysfs_register(struct request_queue *q) @@ -374,7 +374,7 @@ int blk_mq_sysfs_register(struct request_queue *q) struct blk_mq_hw_ctx *hctx; int i, ret = 0;
- mutex_lock(&q->sysfs_lock); + mutex_lock(&q->sysfs_dir_lock); if (!q->mq_sysfs_init_done) goto unlock;
@@ -385,7 +385,7 @@ int blk_mq_sysfs_register(struct request_queue *q) }
unlock: - mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->sysfs_dir_lock);
return ret; } diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 0a7636d24563..b2208b69f04a 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -892,6 +892,7 @@ int blk_register_queue(struct gendisk *disk) int ret; struct device *dev = disk_to_dev(disk); struct request_queue *q = disk->queue; + bool has_elevator = false;
if (WARN_ON(!q)) return -ENXIO; @@ -899,7 +900,6 @@ int blk_register_queue(struct gendisk *disk) WARN_ONCE(blk_queue_registered(q), "%s is registering an already registered queue\n", kobject_name(&dev->kobj)); - queue_flag_set_unlocked(QUEUE_FLAG_REGISTERED, q);
/* * SCSI probing may synchronously create and destroy a lot of @@ -920,8 +920,7 @@ int blk_register_queue(struct gendisk *disk) if (ret) return ret;
- /* Prevent changes through sysfs until registration is completed. */ - mutex_lock(&q->sysfs_lock); + mutex_lock(&q->sysfs_dir_lock);
ret = kobject_add(&q->kobj, kobject_get(&dev->kobj), "%s", "queue"); if (ret < 0) { @@ -934,26 +933,36 @@ int blk_register_queue(struct gendisk *disk) blk_mq_debugfs_register(q); }
- kobject_uevent(&q->kobj, KOBJ_ADD); - - wbt_enable_default(q); - - blk_throtl_register_queue(q); - + /* + * The flag of QUEUE_FLAG_REGISTERED isn't set yet, so elevator + * switch won't happen at all. + */ if (q->request_fn || (q->mq_ops && q->elevator)) { - ret = elv_register_queue(q); + ret = elv_register_queue(q, false); if (ret) { - mutex_unlock(&q->sysfs_lock); - kobject_uevent(&q->kobj, KOBJ_REMOVE); + mutex_unlock(&q->sysfs_dir_lock); kobject_del(&q->kobj); blk_trace_remove_sysfs(dev); kobject_put(&dev->kobj); return ret; } + has_elevator = true; } + + mutex_lock(&q->sysfs_lock); + blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q); + wbt_enable_default(q); + blk_throtl_register_queue(q); + + /* Now everything is ready and send out KOBJ_ADD uevent */ + kobject_uevent(&q->kobj, KOBJ_ADD); + if (has_elevator) + kobject_uevent(&q->elevator->kobj, KOBJ_ADD); + mutex_unlock(&q->sysfs_lock); + ret = 0; unlock: - mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->sysfs_dir_lock); return ret; } EXPORT_SYMBOL_GPL(blk_register_queue); @@ -968,6 +977,7 @@ EXPORT_SYMBOL_GPL(blk_register_queue); void blk_unregister_queue(struct gendisk *disk) { struct request_queue *q = disk->queue; + bool has_elevator;
if (WARN_ON(!q)) return; @@ -982,25 +992,27 @@ void blk_unregister_queue(struct gendisk *disk) * concurrent elv_iosched_store() calls. */ mutex_lock(&q->sysfs_lock); - blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q); + has_elevator = !!q->elevator; + mutex_unlock(&q->sysfs_lock);
+ mutex_lock(&q->sysfs_dir_lock); /* * Remove the sysfs attributes before unregistering the queue data * structures that can be modified through sysfs. */ if (q->mq_ops) blk_mq_unregister_dev(disk_to_dev(disk), q); - mutex_unlock(&q->sysfs_lock);
kobject_uevent(&q->kobj, KOBJ_REMOVE); kobject_del(&q->kobj); blk_trace_remove_sysfs(disk_to_dev(disk));
mutex_lock(&q->sysfs_lock); - if (q->request_fn || (q->mq_ops && q->elevator)) + if (q->request_fn || has_elevator) elv_unregister_queue(q); mutex_unlock(&q->sysfs_lock); + mutex_unlock(&q->sysfs_dir_lock);
kobject_put(&disk_to_dev(disk)->kobj); } diff --git a/block/blk.h b/block/blk.h index 1a5b67b57e6b..ae87e2a5f2bd 100644 --- a/block/blk.h +++ b/block/blk.h @@ -244,7 +244,7 @@ int elevator_init_mq(struct request_queue *q); int elevator_switch_mq(struct request_queue *q, struct elevator_type *new_e); void elevator_exit(struct request_queue *, struct elevator_queue *); -int elv_register_queue(struct request_queue *q); +int elv_register_queue(struct request_queue *q, bool uevent); void elv_unregister_queue(struct request_queue *q);
struct hd_struct *__disk_get_part(struct gendisk *disk, int partno); diff --git a/block/elevator.c b/block/elevator.c index 9bffe4558929..2ff0859e8b35 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -833,13 +833,16 @@ static struct kobj_type elv_ktype = { .release = elevator_release, };
-int elv_register_queue(struct request_queue *q) +/* + * elv_register_queue is called from either blk_register_queue or + * elevator_switch, elevator switch is prevented from being happen + * in the two paths, so it is safe to not hold q->sysfs_lock. + */ +int elv_register_queue(struct request_queue *q, bool uevent) { struct elevator_queue *e = q->elevator; int error;
- lockdep_assert_held(&q->sysfs_lock); - error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched"); if (!error) { struct elv_fs_entry *attr = e->type->elevator_attrs; @@ -850,26 +853,36 @@ int elv_register_queue(struct request_queue *q) attr++; } } - kobject_uevent(&e->kobj, KOBJ_ADD); + if (uevent) + kobject_uevent(&e->kobj, KOBJ_ADD); + + mutex_lock(&q->sysfs_lock); e->registered = 1; if (!e->uses_mq && e->type->ops.sq.elevator_registered_fn) e->type->ops.sq.elevator_registered_fn(q); + mutex_unlock(&q->sysfs_lock); } return error; }
+/* + * elv_unregister_queue is called from either blk_unregister_queue or + * elevator_switch, elevator switch is prevented from being happen + * in the two paths, so it is safe to not hold q->sysfs_lock. + */ void elv_unregister_queue(struct request_queue *q) { - lockdep_assert_held(&q->sysfs_lock); - if (q) { struct elevator_queue *e = q->elevator;
kobject_uevent(&e->kobj, KOBJ_REMOVE); kobject_del(&e->kobj); + + mutex_lock(&q->sysfs_lock); e->registered = 0; /* Re-enable throttling in case elevator disabled it */ wbt_enable_default(q); + mutex_unlock(&q->sysfs_lock); } }
@@ -940,10 +953,32 @@ int elevator_switch_mq(struct request_queue *q, lockdep_assert_held(&q->sysfs_lock);
if (q->elevator) { - if (q->elevator->registered) + if (q->elevator->registered) { + mutex_unlock(&q->sysfs_lock); + + /* + * Concurrent elevator switch can't happen becasue + * sysfs write is always exclusively on same file. + * + * Also the elevator queue won't be freed after + * sysfs_lock is released becasue kobject_del() in + * blk_unregister_queue() waits for completion of + * .store & .show on its attributes. + */ elv_unregister_queue(q); + + mutex_lock(&q->sysfs_lock); + } ioc_clear_queue(q); elevator_exit(q, q->elevator); + + /* + * sysfs_lock may be dropped, so re-check if queue is + * unregistered. If yes, don't switch to new elevator + * any more + */ + if (!blk_queue_registered(q)) + return 0; }
ret = blk_mq_init_sched(q, new_e); @@ -951,7 +986,11 @@ int elevator_switch_mq(struct request_queue *q, goto out;
if (new_e) { - ret = elv_register_queue(q); + mutex_unlock(&q->sysfs_lock); + + ret = elv_register_queue(q, true); + + mutex_lock(&q->sysfs_lock); if (ret) { elevator_exit(q, q->elevator); goto out; @@ -1047,7 +1086,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) if (err) goto fail_init;
- err = elv_register_queue(q); + err = elv_register_queue(q, true); if (err) goto fail_register;
@@ -1067,7 +1106,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) /* switch failed, restore and re-register old elevator */ if (old) { q->elevator = old; - elv_register_queue(q); + elv_register_queue(q, true); blk_queue_bypass_end(q); }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 3a2b34c2c82b..209ba8e7bd31 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -637,6 +637,7 @@ struct request_queue { struct delayed_work requeue_work;
struct mutex sysfs_lock; + struct mutex sysfs_dir_lock;
int bypass_depth; atomic_t mq_freeze_depth;
From: Ming Lei ming.lei@redhat.com
cecf5d87ff20 ("block: split .sysfs_lock into two locks") starts to release & actuire sysfs_lock again during switching elevator. So it isn't enough to prevent switching elevator from happening by simply clearing QUEUE_FLAG_REGISTERED with holding sysfs_lock, because in-progress switch still can move on after re-acquiring the lock, meantime the flag of QUEUE_FLAG_REGISTERED won't get checked.
Fixes this issue by checking 'q->elevator' directly & locklessly after q->kobj is removed in blk_unregister_queue(), this way is safe because q->elevator can't be changed at that time.
Fixes: cecf5d87ff20 ("block: split .sysfs_lock into two locks") Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Mike Snitzer snitzer@redhat.com Cc: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit 0a67b5a926e63ff5492c3c675eab5900580d056d) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/blk-sysfs.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index b2208b69f04a..899987152701 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -977,7 +977,6 @@ EXPORT_SYMBOL_GPL(blk_register_queue); void blk_unregister_queue(struct gendisk *disk) { struct request_queue *q = disk->queue; - bool has_elevator;
if (WARN_ON(!q)) return; @@ -993,7 +992,6 @@ void blk_unregister_queue(struct gendisk *disk) */ mutex_lock(&q->sysfs_lock); blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q); - has_elevator = !!q->elevator; mutex_unlock(&q->sysfs_lock);
mutex_lock(&q->sysfs_dir_lock); @@ -1009,7 +1007,11 @@ void blk_unregister_queue(struct gendisk *disk) blk_trace_remove_sysfs(disk_to_dev(disk));
mutex_lock(&q->sysfs_lock); - if (q->request_fn || has_elevator) + /* + * q->kobj has been removed, so it is safe to check if elevator + * exists without holding q->sysfs_lock. + */ + if (q->request_fn || q->elevator) elv_unregister_queue(q); mutex_unlock(&q->sysfs_lock); mutex_unlock(&q->sysfs_dir_lock);
From: Ming Lei ming.lei@redhat.com
cecf5d87ff20 ("block: split .sysfs_lock into two locks") starts to release & acquire sysfs_lock before registering/un-registering elevator queue during switching elevator for avoiding potential deadlock from showing & storing 'queue/iosched' attributes and removing elevator's kobject.
Turns out there isn't such deadlock because 'q->sysfs_lock' isn't required in .show & .store of queue/iosched's attributes, and just elevator's sysfs lock is acquired in elv_iosched_store() and elv_iosched_show(). So it is safe to hold queue's sysfs lock when registering/un-registering elevator queue.
The biggest issue is that commit cecf5d87ff20 assumes that concurrent write on 'queue/scheduler' can't happen. However, this assumption isn't true, because kernfs_fop_write() only guarantees that concurrent write aren't called on the same open file, but the write could be from different open on the file. So we can't release & re-acquire queue's sysfs lock during switching elevator, otherwise use-after-free on elevator could be triggered.
Fixes the issue by not releasing queue's sysfs lock during switching elevator.
Fixes: cecf5d87ff20 ("block: split .sysfs_lock into two locks") Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Mike Snitzer snitzer@redhat.com Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk (jwang:cherry picked from commit b89f625e28d44552083f43752f62d8621ded0a04 adjust ctx for 4.19) Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- block/blk-sysfs.c | 3 ++- block/elevator.c | 31 +------------------------------ 2 files changed, 3 insertions(+), 31 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 899987152701..07494deb1a26 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -933,6 +933,7 @@ int blk_register_queue(struct gendisk *disk) blk_mq_debugfs_register(q); }
+ mutex_lock(&q->sysfs_lock); /* * The flag of QUEUE_FLAG_REGISTERED isn't set yet, so elevator * switch won't happen at all. @@ -940,6 +941,7 @@ int blk_register_queue(struct gendisk *disk) if (q->request_fn || (q->mq_ops && q->elevator)) { ret = elv_register_queue(q, false); if (ret) { + mutex_unlock(&q->sysfs_lock); mutex_unlock(&q->sysfs_dir_lock); kobject_del(&q->kobj); blk_trace_remove_sysfs(dev); @@ -949,7 +951,6 @@ int blk_register_queue(struct gendisk *disk) has_elevator = true; }
- mutex_lock(&q->sysfs_lock); blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q); wbt_enable_default(q); blk_throtl_register_queue(q); diff --git a/block/elevator.c b/block/elevator.c index 2ff0859e8b35..5b51bc5fad9f 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -856,11 +856,9 @@ int elv_register_queue(struct request_queue *q, bool uevent) if (uevent) kobject_uevent(&e->kobj, KOBJ_ADD);
- mutex_lock(&q->sysfs_lock); e->registered = 1; if (!e->uses_mq && e->type->ops.sq.elevator_registered_fn) e->type->ops.sq.elevator_registered_fn(q); - mutex_unlock(&q->sysfs_lock); } return error; } @@ -878,11 +876,9 @@ void elv_unregister_queue(struct request_queue *q) kobject_uevent(&e->kobj, KOBJ_REMOVE); kobject_del(&e->kobj);
- mutex_lock(&q->sysfs_lock); e->registered = 0; /* Re-enable throttling in case elevator disabled it */ wbt_enable_default(q); - mutex_unlock(&q->sysfs_lock); } }
@@ -953,32 +949,11 @@ int elevator_switch_mq(struct request_queue *q, lockdep_assert_held(&q->sysfs_lock);
if (q->elevator) { - if (q->elevator->registered) { - mutex_unlock(&q->sysfs_lock); - - /* - * Concurrent elevator switch can't happen becasue - * sysfs write is always exclusively on same file. - * - * Also the elevator queue won't be freed after - * sysfs_lock is released becasue kobject_del() in - * blk_unregister_queue() waits for completion of - * .store & .show on its attributes. - */ + if (q->elevator->registered) elv_unregister_queue(q);
- mutex_lock(&q->sysfs_lock); - } ioc_clear_queue(q); elevator_exit(q, q->elevator); - - /* - * sysfs_lock may be dropped, so re-check if queue is - * unregistered. If yes, don't switch to new elevator - * any more - */ - if (!blk_queue_registered(q)) - return 0; }
ret = blk_mq_init_sched(q, new_e); @@ -986,11 +961,7 @@ int elevator_switch_mq(struct request_queue *q, goto out;
if (new_e) { - mutex_unlock(&q->sysfs_lock); - ret = elv_register_queue(q, true); - - mutex_lock(&q->sysfs_lock); if (ret) { elevator_exit(q, q->elevator); goto out;
From: Xiao Ni xni@redhat.com
One customer reports a crash problem which causes by flush request. It triggers a warning before crash.
/* new request after previous flush is completed */ if (ktime_after(req_start, mddev->prev_flush_start)) { WARN_ON(mddev->flush_bio); mddev->flush_bio = bio; bio = NULL; }
The WARN_ON is triggered. We use spin lock to protect prev_flush_start and flush_bio in md_flush_request. But there is no lock protection in md_submit_flush_data. It can set flush_bio to NULL first because of compiler reordering write instructions.
For example, flush bio1 sets flush bio to NULL first in md_submit_flush_data. An interrupt or vmware causing an extended stall happen between updating flush_bio and prev_flush_start. Because flush_bio is NULL, flush bio2 can get the lock and submit to underlayer disks. Then flush bio1 updates prev_flush_start after the interrupt or extended stall.
Then flush bio3 enters in md_flush_request. The start time req_start is behind prev_flush_start. The flush_bio is not NULL(flush bio2 hasn't finished). So it can trigger the WARN_ON now. Then it calls INIT_WORK again. INIT_WORK() will re-initialize the list pointers in the work_struct, which then can result in a corrupted work list and the work_struct queued a second time. With the work list corrupted, it can lead in invalid work items being used and cause a crash in process_one_work.
We need to make sure only one flush bio can be handled at one same time. So add spin lock in md_submit_flush_data to protect prev_flush_start and flush_bio in an atomic way.
Reviewed-by: David Jeffery djeffery@redhat.com Signed-off-by: Xiao Ni xni@redhat.com Signed-off-by: Song Liu songliubraving@fb.com [jwang: backport dc5d17a3c39b06aef866afca19245a9cfb533a79 to 4.19] Signed-off-by: Jack Wang jinpu.wang@cloud.ionos.com --- drivers/md/md.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/md/md.c b/drivers/md/md.c index 80ca13594c18..09f0d8e70b70 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -474,8 +474,10 @@ static void md_submit_flush_data(struct work_struct *ws) * could wait for this and below md_handle_request could wait for those * bios because of suspend check */ + spin_lock_irq(&mddev->lock); mddev->last_flush = mddev->start_flush; mddev->flush_bio = NULL; + spin_unlock_irq(&mddev->lock); wake_up(&mddev->sb_wait);
if (bio->bi_iter.bi_size == 0) {
On Wed, Feb 03, 2021 at 02:20:22PM +0100, Jack Wang wrote:
From: Xiao Ni xni@redhat.com
One customer reports a crash problem which causes by flush request. It triggers a warning before crash.
/* new request after previous flush is completed */ if (ktime_after(req_start, mddev->prev_flush_start)) { WARN_ON(mddev->flush_bio); mddev->flush_bio = bio; bio = NULL; }The WARN_ON is triggered. We use spin lock to protect prev_flush_start and flush_bio in md_flush_request. But there is no lock protection in md_submit_flush_data. It can set flush_bio to NULL first because of compiler reordering write instructions.
For example, flush bio1 sets flush bio to NULL first in md_submit_flush_data. An interrupt or vmware causing an extended stall happen between updating flush_bio and prev_flush_start. Because flush_bio is NULL, flush bio2 can get the lock and submit to underlayer disks. Then flush bio1 updates prev_flush_start after the interrupt or extended stall.
Then flush bio3 enters in md_flush_request. The start time req_start is behind prev_flush_start. The flush_bio is not NULL(flush bio2 hasn't finished). So it can trigger the WARN_ON now. Then it calls INIT_WORK again. INIT_WORK() will re-initialize the list pointers in the work_struct, which then can result in a corrupted work list and the work_struct queued a second time. With the work list corrupted, it can lead in invalid work items being used and cause a crash in process_one_work.
We need to make sure only one flush bio can be handled at one same time. So add spin lock in md_submit_flush_data to protect prev_flush_start and flush_bio in an atomic way.
Reviewed-by: David Jeffery djeffery@redhat.com Signed-off-by: Xiao Ni xni@redhat.com Signed-off-by: Song Liu songliubraving@fb.com [jwang: backport dc5d17a3c39b06aef866afca19245a9cfb533a79 to 4.19]
I can not take patches backported to older kernels that "skip" kernel releases.
For example, if I take this into 4.19.y, and then someone moves to 5.4 or 5.10, they will hit the same issue.
So please provide a backported series for all affected releases, back as far as you want, but never skip releases.
I can't take this series, I'll drop it for now and wait for an updated set of patches.
thanks,
greg k-h
On Thu, Feb 4, 2021 at 4:12 PM Greg KH gregkh@linuxfoundation.org wrote:
On Wed, Feb 03, 2021 at 02:20:22PM +0100, Jack Wang wrote:
From: Xiao Ni xni@redhat.com
One customer reports a crash problem which causes by flush request. It triggers a warning before crash.
/* new request after previous flush is completed */ if (ktime_after(req_start, mddev->prev_flush_start)) { WARN_ON(mddev->flush_bio); mddev->flush_bio = bio; bio = NULL; }The WARN_ON is triggered. We use spin lock to protect prev_flush_start and flush_bio in md_flush_request. But there is no lock protection in md_submit_flush_data. It can set flush_bio to NULL first because of compiler reordering write instructions.
For example, flush bio1 sets flush bio to NULL first in md_submit_flush_data. An interrupt or vmware causing an extended stall happen between updating flush_bio and prev_flush_start. Because flush_bio is NULL, flush bio2 can get the lock and submit to underlayer disks. Then flush bio1 updates prev_flush_start after the interrupt or extended stall.
Then flush bio3 enters in md_flush_request. The start time req_start is behind prev_flush_start. The flush_bio is not NULL(flush bio2 hasn't finished). So it can trigger the WARN_ON now. Then it calls INIT_WORK again. INIT_WORK() will re-initialize the list pointers in the work_struct, which then can result in a corrupted work list and the work_struct queued a second time. With the work list corrupted, it can lead in invalid work items being used and cause a crash in process_one_work.
We need to make sure only one flush bio can be handled at one same time. So add spin lock in md_submit_flush_data to protect prev_flush_start and flush_bio in an atomic way.
Reviewed-by: David Jeffery djeffery@redhat.com Signed-off-by: Xiao Ni xni@redhat.com Signed-off-by: Song Liu songliubraving@fb.com [jwang: backport dc5d17a3c39b06aef866afca19245a9cfb533a79 to 4.19]
I can not take patches backported to older kernels that "skip" kernel releases.
For example, if I take this into 4.19.y, and then someone moves to 5.4 or 5.10, they will hit the same issue.
So please provide a backported series for all affected releases, back as far as you want, but never skip releases.
I can't take this series, I'll drop it for now and wait for an updated set of patches.
thanks,
greg k-h
Hi Greg,
Thanks for reply, only this patch should be backported also to 5.4/5.10, this backport can be applied cleanly to stable/linux-5.4.y and stable/linux-5.10.y,
I will send the backport for them later today!
Thanks!
J
linux-stable-mirror@lists.linaro.org
-
Greg KH -
Jack Wang -
Jinpu Wang