The patch below does not apply to the 5.11-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From eb85890b29e4d7ae1accdcfba35ed8b16ba9fb97 Mon Sep 17 00:00:00 2001

From: Jens Axboe axboe@kernel.dk Date: Thu, 25 Feb 2021 10:13:29 -0700 Subject: [PATCH] io_uring: ensure SQPOLL startup is triggered before error shutdown

syzbot reports the following hang:

INFO: task syz-executor.0:12538 can't die for more than 143 seconds. task:syz-executor.0 state:D stack:28352 pid:12538 ppid: 8423 flags:0x00004004 Call Trace: context_switch kernel/sched/core.c:4324 [inline] __schedule+0x90c/0x21a0 kernel/sched/core.c:5075 schedule+0xcf/0x270 kernel/sched/core.c:5154 schedule_timeout+0x1db/0x250 kernel/time/timer.c:1868 do_wait_for_common kernel/sched/completion.c:85 [inline] __wait_for_common kernel/sched/completion.c:106 [inline] wait_for_common kernel/sched/completion.c:117 [inline] wait_for_completion+0x168/0x270 kernel/sched/completion.c:138 io_sq_thread_finish+0x96/0x580 fs/io_uring.c:7152 io_sq_offload_create fs/io_uring.c:7929 [inline] io_uring_create fs/io_uring.c:9465 [inline] io_uring_setup+0x1fb2/0x2c20 fs/io_uring.c:9550 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x44/0xae

which is due to exiting after the SQPOLL thread has been created, but hasn't been started yet. Ensure that we always complete the startup side when waiting for it to exit.

Reported-by: syzbot+c927c937cba8ef66dd4a@syzkaller.appspotmail.com Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/fs/io_uring.c b/fs/io_uring.c index fbc85afa9a87..ef743594d34a 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -7141,6 +7141,7 @@ static void io_sq_thread_finish(struct io_ring_ctx *ctx) struct io_sq_data *sqd = ctx->sq_data;

if (sqd) { + complete(&sqd->startup); if (sqd->thread) { wait_for_completion(&ctx->sq_thread_comp); io_sq_thread_park(sqd); @@ -7927,7 +7928,7 @@ static void io_sq_offload_start(struct io_ring_ctx *ctx) { struct io_sq_data *sqd = ctx->sq_data;

- if ((ctx->flags & IORING_SETUP_SQPOLL) && sqd->thread) + if (ctx->flags & IORING_SETUP_SQPOLL) complete(&sqd->startup); }