rwb_enabled() can't be changed when there is any inflight IO.

wbt_disable_default() may set rwb->wb_normal as zero, however the blk_stat timer may still be pending, and the timer function will update wrb->wb_normal again.

This patch introduces blk_stat_deactivate() and applies it in wbt_disable_default(), then the following IO hang triggered when running parted & switching io scheduler can be fixed:

[ 369.937806] INFO: task parted:3645 blocked for more than 120 seconds. [ 369.938941] Not tainted 4.20.0-rc6-00284-g906c801e5248 #498 [ 369.939797] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 369.940768] parted D 0 3645 3239 0x00000000 [ 369.941500] Call Trace: [ 369.941874] ? __schedule+0x6d9/0x74c [ 369.942392] ? wbt_done+0x5e/0x5e [ 369.942864] ? wbt_cleanup_cb+0x16/0x16 [ 369.943404] ? wbt_done+0x5e/0x5e [ 369.943874] schedule+0x67/0x78 [ 369.944298] io_schedule+0x12/0x33 [ 369.944771] rq_qos_wait+0xb5/0x119 [ 369.945193] ? karma_partition+0x1c2/0x1c2 [ 369.945691] ? wbt_cleanup_cb+0x16/0x16 [ 369.946151] wbt_wait+0x85/0xb6 [ 369.946540] __rq_qos_throttle+0x23/0x2f [ 369.947014] blk_mq_make_request+0xe6/0x40a [ 369.947518] generic_make_request+0x192/0x2fe [ 369.948042] ? submit_bio+0x103/0x11f [ 369.948486] ? __radix_tree_lookup+0x35/0xb5 [ 369.949011] submit_bio+0x103/0x11f [ 369.949436] ? blkg_lookup_slowpath+0x25/0x44 [ 369.949962] submit_bio_wait+0x53/0x7f [ 369.950469] blkdev_issue_flush+0x8a/0xae [ 369.951032] blkdev_fsync+0x2f/0x3a [ 369.951502] do_fsync+0x2e/0x47 [ 369.951887] __x64_sys_fsync+0x10/0x13 [ 369.952374] do_syscall_64+0x89/0x149 [ 369.952819] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 369.953492] RIP: 0033:0x7f95a1e729d4 [ 369.953996] Code: Bad RIP value. [ 369.954456] RSP: 002b:00007ffdb570dd48 EFLAGS: 00000246 ORIG_RAX: 000000000000004a [ 369.955506] RAX: ffffffffffffffda RBX: 000055c2139c6be0 RCX: 00007f95a1e729d4 [ 369.956389] RDX: 0000000000000001 RSI: 0000000000001261 RDI: 0000000000000004 [ 369.957325] RBP: 0000000000000002 R08: 0000000000000000 R09: 000055c2139c6ce0 [ 369.958199] R10: 0000000000000000 R11: 0000000000000246 R12: 000055c2139c0380 [ 369.959143] R13: 0000000000000004 R14: 0000000000000100 R15: 0000000000000008

Cc: stable@vger.kernel.org Cc: Paolo Valente paolo.valente@linaro.org Signed-off-by: Ming Lei ming.lei@redhat.com --- block/blk-stat.h | 5 +++++ block/blk-wbt.c | 4 +++- 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/block/blk-stat.h b/block/blk-stat.h index f4a1568e81a4..17b47a86eefb 100644 --- a/block/blk-stat.h +++ b/block/blk-stat.h @@ -145,6 +145,11 @@ static inline void blk_stat_activate_nsecs(struct blk_stat_callback *cb, mod_timer(&cb->timer, jiffies + nsecs_to_jiffies(nsecs)); }

+static inline void blk_stat_deactivate(struct blk_stat_callback *cb) +{ + del_timer_sync(&cb->timer); +} + /** * blk_stat_activate_msecs() - Gather block statistics during a time window in * milliseconds. diff --git a/block/blk-wbt.c b/block/blk-wbt.c index 8ac93fcbaa2e..0c62bf4eca75 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -760,8 +760,10 @@ void wbt_disable_default(struct request_queue *q) if (!rqos) return; rwb = RQWB(rqos); - if (rwb->enable_state == WBT_STATE_ON_DEFAULT) + if (rwb->enable_state == WBT_STATE_ON_DEFAULT) { + blk_stat_deactivate(rwb->cb); rwb->wb_normal = 0; + } } EXPORT_SYMBOL_GPL(wbt_disable_default);