Commit 8eb06d7e authored Jun 30, 2020 by Pavel Begunkov Committed by Jens Axboe Jun 30, 2020

io_uring: fix missing ->mm on exit



There is a fancy bug, where exiting user task may not have ->mm,
that makes task_works to try to do kthread_use_mm(ctx->sqo_mm).

Don't do that if sqo_mm is NULL.

[  290.460558] WARNING: CPU: 6 PID: 150933 at kernel/kthread.c:1238
	kthread_use_mm+0xf3/0x110
[  290.460579] CPU: 6 PID: 150933 Comm: read-write2 Tainted: G
	I E     5.8.0-rc2-00066-g9b21720607cf #531
[  290.460580] RIP: 0010:kthread_use_mm+0xf3/0x110
...
[  290.460584] Call Trace:
[  290.460584]  __io_sq_thread_acquire_mm.isra.0.part.0+0x25/0x30
[  290.460584]  __io_req_task_submit+0x64/0x80
[  290.460584]  io_req_task_submit+0x15/0x20
[  290.460585]  task_work_run+0x67/0xa0
[  290.460585]  do_exit+0x35d/0xb70
[  290.460585]  do_group_exit+0x43/0xa0
[  290.460585]  get_signal+0x140/0x900
[  290.460586]  do_signal+0x37/0x780
[  290.460586]  __prepare_exit_to_usermode+0x126/0x1c0
[  290.460586]  __syscall_return_slowpath+0x3b/0x1c0
[  290.460587]  do_syscall_64+0x5f/0xa0
[  290.460587]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

following with faults.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 3fa5e0f3

fs/io_uring.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -958,7 +958,7 @@ static void io_sq_thread_drop_mm(struct io_ring_ctx *ctx)
		static int __io_sq_thread_acquire_mm(struct io_ring_ctx *ctx)
		{
		if (!current->mm) {
		if (unlikely(!mmget_not_zero(ctx->sqo_mm)))
		if (unlikely(!ctx->sqo_mm \|\| !mmget_not_zero(ctx->sqo_mm)))
		return -EFAULT;
		kthread_use_mm(ctx->sqo_mm);
		}
		@@ -7216,10 +7216,10 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
		{
		int ret;

		if (ctx->flags & IORING_SETUP_SQPOLL) {
		mmgrab(current->mm);
		ctx->sqo_mm = current->mm;

		if (ctx->flags & IORING_SETUP_SQPOLL) {
		ret = -EPERM;
		if (!capable(CAP_SYS_ADMIN))
		goto err;
		@@ -7263,8 +7263,10 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
		return 0;
		err:
		io_finish_async(ctx);
		if (ctx->sqo_mm) {
		mmdrop(ctx->sqo_mm);
		ctx->sqo_mm = NULL;
		}
		return ret;
		}

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