[ldv-project] [PATCH 5.10 2/2] io_uring; fix files cancel hangs

[Fedor Pchelkin]

From: Pavel Begunkov <asml.silence at gmail.com>

We park SQPOLL task before going into io_uring_cancel_files(), so the
task won't run task_works including those that might be important for
the cancellation passes. In this case it's io_poll_remove_one(), which
frees requests via io_put_req_deferred().

Unpark it for while waiting, it's ok as we disable submissions
beforehand, so no new will be generated.

INFO: task syz-executor893:8493 blocked for more than 143 seconds.
Call Trace:
 context_switch kernel/sched/core.c:4327 [inline]
 __schedule+0x90c/0x21a0 kernel/sched/core.c:5078
 schedule+0xcf/0x270 kernel/sched/core.c:5157
 io_uring_cancel_files fs/io_uring.c:8912 [inline]
 io_uring_cancel_task_requests+0xe70/0x11a0 fs/io_uring.c:8979
 __io_uring_files_cancel+0x110/0x1b0 fs/io_uring.c:9067
 io_uring_files_cancel include/linux/io_uring.h:51 [inline]
 do_exit+0x2fe/0x2ae0 kernel/exit.c:780
 do_group_exit+0x125/0x310 kernel/exit.c:922
 __do_sys_exit_group kernel/exit.c:933 [inline]
 __se_sys_exit_group kernel/exit.c:931 [inline]
 __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:931
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Cc: stable at xxxxxxxxxxxxxxx # 5.5+
Reported-by: syzbot+695b03d82fa8e4901b06 at xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Pavel Begunkov <asml.silence at gmail.com>
Signed-off-by: Fedor Pchelkin <pchelkin at ispras.ru>
---
 fs/io_uring.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 25f2b87673bf..6a8b5785e783 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8685,11 +8685,15 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 		/* cancellations _may_ trigger task work */
 		io_run_task_work();
 
+		if (ctx->sq_data)
+			io_sq_thread_unpark(ctx->sq_data);
 		prepare_to_wait(&task->io_uring->wait, &wait,
 				TASK_UNINTERRUPTIBLE);
 		if (inflight == io_uring_count_inflight(ctx, task, files))
 			schedule();
 		finish_wait(&task->io_uring->wait, &wait);
+		if (ctx->sq_data)
+			io_sq_thread_park(ctx->sq_data);
 	}
 }
 
-- 
2.25.1