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From: Pavel Begunkov <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Subject: [PATCH 4/8] io_uring: fix missing ->mm on exit
Date: Tue, 30 Jun 2020 15:20:39 +0300	[thread overview]
Message-ID: <0f2b8d6cdd39a965f70d1d4b22de5570a53691f8.1593519186.git.asml.silence@gmail.com> (raw)
In-Reply-To: <[email protected]>

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 <[email protected]>
---
 fs/io_uring.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 776f593a5bf3..c7986c27272e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -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);
 	}
@@ -7212,10 +7212,10 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
 {
 	int ret;
 
-	mmgrab(current->mm);
-	ctx->sqo_mm = current->mm;
-
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		mmgrab(current->mm);
+		ctx->sqo_mm = current->mm;
+
 		ret = -EPERM;
 		if (!capable(CAP_SYS_ADMIN))
 			goto err;
@@ -7259,8 +7259,10 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
 	return 0;
 err:
 	io_finish_async(ctx);
-	mmdrop(ctx->sqo_mm);
-	ctx->sqo_mm = NULL;
+	if (ctx->sqo_mm) {
+		mmdrop(ctx->sqo_mm);
+		ctx->sqo_mm = NULL;
+	}
 	return ret;
 }
 
-- 
2.24.0


  parent reply	other threads:[~2020-06-30 12:22 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-30 12:20 [PATCH 0/8] iopoll and task_work fixes Pavel Begunkov
2020-06-30 12:20 ` [PATCH 1/8] io_uring: fix io_fail_links() locking Pavel Begunkov
2020-06-30 14:38   ` Jens Axboe
2020-06-30 14:45     ` Pavel Begunkov
2020-06-30 12:20 ` [PATCH 2/8] io_uring: fix commit_cqring() locking in iopoll Pavel Begunkov
2020-06-30 14:04   ` Jens Axboe
2020-06-30 14:36     ` Pavel Begunkov
2020-06-30 14:46       ` Jens Axboe
2020-06-30 15:00         ` Pavel Begunkov
2020-06-30 15:33           ` Jens Axboe
2020-06-30 12:20 ` [PATCH 3/8] io_uring: fix ignoring eventfd " Pavel Begunkov
2020-06-30 12:20 ` Pavel Begunkov [this message]
2020-06-30 12:20 ` [PATCH 5/8] io_uring: don't fail iopoll requeue without ->mm Pavel Begunkov
2020-06-30 12:20 ` [PATCH 6/8] io_uring: fix NULL mm in io_poll_task_func() Pavel Begunkov
2020-06-30 12:20 ` [PATCH 7/8] io_uring: simplify io_async_task_func() Pavel Begunkov
2020-06-30 12:20 ` [PATCH 8/8] io_uring: optimise io_req_find_next() fast check Pavel Begunkov
2020-06-30 12:39 ` [PATCH 0/8] iopoll and task_work fixes Pavel Begunkov

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