[ 97.866748] a.out/2890 is trying to acquire lock: [ 97.867829] ffff8881046763e8 (&ctx->uring_lock){+.+.}-{3:3}, at: io_wq_submit_work+0x155/0x240 [ 97.869735] [ 97.869735] but task is already holding lock: [ 97.871033] ffff88810dfe0be8 (&ctx->uring_lock){+.+.}-{3:3}, at: __x64_sys_io_uring_enter+0x3f0/0x5b0 [ 97.873074] [ 97.873074] other info that might help us debug this: [ 97.874520] Possible unsafe locking scenario: [ 97.874520] [ 97.875845] CPU0 [ 97.876440] ---- [ 97.877048] lock(&ctx->uring_lock); [ 97.877961] lock(&ctx->uring_lock); [ 97.878881] [ 97.878881] *** DEADLOCK *** [ 97.878881] [ 97.880341] May be due to missing lock nesting notation [ 97.880341] [ 97.881952] 1 lock held by a.out/2890: [ 97.882873] #0: ffff88810dfe0be8 (&ctx->uring_lock){+.+.}-{3:3}, at: __x64_sys_io_uring_enter+0x3f0/0x5b0 [ 97.885108] [ 97.885108] stack backtrace: [ 97.890457] Call Trace: [ 97.891121] dump_stack+0xac/0xe3 [ 97.891972] __lock_acquire+0xab6/0x13a0 [ 97.892940] lock_acquire+0x2c3/0x390 [ 97.894894] __mutex_lock+0xae/0x9f0 [ 97.901101] io_wq_submit_work+0x155/0x240 [ 97.902112] io_wq_cancel_cb+0x162/0x490 [ 97.904126] io_async_find_and_cancel+0x3b/0x140 [ 97.905247] io_issue_sqe+0x86d/0x13e0 [ 97.909122] __io_queue_sqe+0x10b/0x550 [ 97.913971] io_queue_sqe+0x235/0x470 [ 97.914894] io_submit_sqes+0xcce/0xf10 [ 97.917872] __x64_sys_io_uring_enter+0x3fb/0x5b0 [ 97.921424] do_syscall_64+0x2d/0x40 [ 97.922329] entry_SYSCALL_64_after_hwframe+0x44/0xa9

While holding uring_lock, e.g. from inline execution, async cancel request may attempt cancellations through io_wq_submit_work, which may try to grab a lock. Delay it to task_work, so we do it from a clean context and don't have to worry about locking.

Cc: stable@vger.kernel.org # 5.5+ Fixes: c07e6719511e ("io_uring: hold uring_lock while completing failed polled io in io_wq_submit_work()") Reported-by: Abaci abaci@linux.alibaba.com Reported-by: Hao Xu haoxu@linux.alibaba.com Signed-off-by: Pavel Begunkov asml.silence@gmail.com --- fs/io_uring.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c index 2fdfe5fa00b0..8dab07f42b34 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -2337,7 +2337,9 @@ static void io_req_task_cancel(struct callback_head *cb) struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); struct io_ring_ctx *ctx = req->ctx;

+ mutex_lock(&ctx->uring_lock); __io_req_task_cancel(req, -ECANCELED); + mutex_unlock(&ctx->uring_lock); percpu_ref_put(&ctx->refs); }

@@ -6426,8 +6428,13 @@ static void io_wq_submit_work(struct io_wq_work *work) if (timeout) io_queue_linked_timeout(timeout);

- if (work->flags & IO_WQ_WORK_CANCEL) - ret = -ECANCELED; + if (work->flags & IO_WQ_WORK_CANCEL) { + /* io-wq is going to take down one */ + refcount_inc(&req->refs); + percpu_ref_get(&req->ctx->refs); + io_req_task_work_add_fallback(req, io_req_task_cancel); + return; + }

if (!ret) { do {