From: Hillf Danton hdanton@sina.com
commit 4afdb733b1606c6cb86e7833f9335f4870cf7ddd upstream.
A case of task hung was reported by syzbot,
INFO: task syz-executor975:9880 blocked for more than 143 seconds. Not tainted 5.6.0-rc6-syzkaller #0 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor975 D27576 9880 9878 0x80004000 Call Trace: schedule+0xd0/0x2a0 kernel/sched/core.c:4154 schedule_timeout+0x6db/0xba0 kernel/time/timer.c:1871 do_wait_for_common kernel/sched/completion.c:83 [inline] __wait_for_common kernel/sched/completion.c:104 [inline] wait_for_common kernel/sched/completion.c:115 [inline] wait_for_completion+0x26a/0x3c0 kernel/sched/completion.c:136 io_queue_file_removal+0x1af/0x1e0 fs/io_uring.c:5826 __io_sqe_files_update.isra.0+0x3a1/0xb00 fs/io_uring.c:5867 io_sqe_files_update fs/io_uring.c:5918 [inline] __io_uring_register+0x377/0x2c00 fs/io_uring.c:7131 __do_sys_io_uring_register fs/io_uring.c:7202 [inline] __se_sys_io_uring_register fs/io_uring.c:7184 [inline] __x64_sys_io_uring_register+0x192/0x560 fs/io_uring.c:7184 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe
and bisect pointed to 05f3fb3c5397 ("io_uring: avoid ring quiesce for fixed file set unregister and update").
It is down to the order that we wait for work done before flushing it while nobody is likely going to wake us up.
We can drop that completion on stack as flushing work itself is a sync operation we need and no more is left behind it.
To that end, io_file_put::done is re-used for indicating if it can be freed in the workqueue worker context.
Reported-and-Inspired-by: syzbot syzbot+538d1957ce178382a394@syzkaller.appspotmail.com Signed-off-by: Hillf Danton hdanton@sina.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
Rename ->done to ->free_pfile
Signed-off-by: Jens Axboe axboe@kernel.dk
--- fs/io_uring.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-)
--- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -5607,7 +5607,7 @@ static void io_ring_file_put(struct io_r struct io_file_put { struct llist_node llist; struct file *file; - struct completion *done; + bool free_pfile; };
static void io_ring_file_ref_flush(struct fixed_file_data *data) @@ -5618,9 +5618,7 @@ static void io_ring_file_ref_flush(struc while ((node = llist_del_all(&data->put_llist)) != NULL) { llist_for_each_entry_safe(pfile, tmp, node, llist) { io_ring_file_put(data->ctx, pfile->file); - if (pfile->done) - complete(pfile->done); - else + if (pfile->free_pfile) kfree(pfile); } } @@ -5820,7 +5818,6 @@ static bool io_queue_file_removal(struct struct file *file) { struct io_file_put *pfile, pfile_stack; - DECLARE_COMPLETION_ONSTACK(done);
/* * If we fail allocating the struct we need for doing async reomval @@ -5829,15 +5826,15 @@ static bool io_queue_file_removal(struct pfile = kzalloc(sizeof(*pfile), GFP_KERNEL); if (!pfile) { pfile = &pfile_stack; - pfile->done = &done; - } + pfile->free_pfile = false; + } else + pfile->free_pfile = true;
pfile->file = file; llist_add(&pfile->llist, &data->put_llist);
if (pfile == &pfile_stack) { percpu_ref_switch_to_atomic(&data->refs, io_atomic_switch); - wait_for_completion(&done); flush_work(&data->ref_work); return false; }