From: Jens Axboe axboe@kernel.dk
commit c018db4a57f3e31a9cb24d528e9f094eda89a499 upstream.
Ammar reports that he's seeing a lockdep splat on running test/rsrc_tags from the regression suite:
====================================================== WARNING: possible circular locking dependency detected 5.14.0-rc3-bluetea-test-00249-gc7d102232649 #5 Tainted: G OE ------------------------------------------------------ kworker/2:4/2684 is trying to acquire lock: ffff88814bb1c0a8 (&ctx->uring_lock){+.+.}-{3:3}, at: io_rsrc_put_work+0x13d/0x1a0
but task is already holding lock: ffffc90001c6be70 ((work_completion)(&(&ctx->rsrc_put_work)->work)){+.+.}-{0:0}, at: process_one_work+0x1bc/0x530
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 ((work_completion)(&(&ctx->rsrc_put_work)->work)){+.+.}-{0:0}: __flush_work+0x31b/0x490 io_rsrc_ref_quiesce.part.0.constprop.0+0x35/0xb0 __do_sys_io_uring_register+0x45b/0x1060 do_syscall_64+0x35/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae
-> #0 (&ctx->uring_lock){+.+.}-{3:3}: __lock_acquire+0x119a/0x1e10 lock_acquire+0xc8/0x2f0 __mutex_lock+0x86/0x740 io_rsrc_put_work+0x13d/0x1a0 process_one_work+0x236/0x530 worker_thread+0x52/0x3b0 kthread+0x135/0x160 ret_from_fork+0x1f/0x30
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock((work_completion)(&(&ctx->rsrc_put_work)->work)); lock(&ctx->uring_lock); lock((work_completion)(&(&ctx->rsrc_put_work)->work)); lock(&ctx->uring_lock);
*** DEADLOCK ***
2 locks held by kworker/2:4/2684: #0: ffff88810004d938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1bc/0x530 #1: ffffc90001c6be70 ((work_completion)(&(&ctx->rsrc_put_work)->work)){+.+.}-{0:0}, at: process_one_work+0x1bc/0x530
stack backtrace: CPU: 2 PID: 2684 Comm: kworker/2:4 Tainted: G OE 5.14.0-rc3-bluetea-test-00249-gc7d102232649 #5 Hardware name: Acer Aspire ES1-421/OLVIA_BE, BIOS V1.05 07/02/2015 Workqueue: events io_rsrc_put_work Call Trace: dump_stack_lvl+0x6a/0x9a check_noncircular+0xfe/0x110 __lock_acquire+0x119a/0x1e10 lock_acquire+0xc8/0x2f0 ? io_rsrc_put_work+0x13d/0x1a0 __mutex_lock+0x86/0x740 ? io_rsrc_put_work+0x13d/0x1a0 ? io_rsrc_put_work+0x13d/0x1a0 ? io_rsrc_put_work+0x13d/0x1a0 ? process_one_work+0x1ce/0x530 io_rsrc_put_work+0x13d/0x1a0 process_one_work+0x236/0x530 worker_thread+0x52/0x3b0 ? process_one_work+0x530/0x530 kthread+0x135/0x160 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x1f/0x30
which is due to holding the ctx->uring_lock when flushing existing pending work, while the pending work flushing may need to grab the uring lock if we're using IOPOLL.
Fix this by dropping the uring_lock a bit earlier as part of the flush.
Cc: stable@vger.kernel.org Link: https://github.com/axboe/liburing/issues/404 Tested-by: Ammar Faizi ammarfaizi2@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/io_uring.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -7166,17 +7166,19 @@ static int io_rsrc_ref_quiesce(struct io /* kill initial ref, already quiesced if zero */ if (atomic_dec_and_test(&data->refs)) break; + mutex_unlock(&ctx->uring_lock); flush_delayed_work(&ctx->rsrc_put_work); ret = wait_for_completion_interruptible(&data->done); - if (!ret) + if (!ret) { + mutex_lock(&ctx->uring_lock); break; + }
atomic_inc(&data->refs); /* wait for all works potentially completing data->done */ flush_delayed_work(&ctx->rsrc_put_work); reinit_completion(&data->done);
- mutex_unlock(&ctx->uring_lock); ret = io_run_task_work_sig(); mutex_lock(&ctx->uring_lock); } while (ret >= 0);