Linux-Fsdevel Archive on
help / color / mirror / Atom feed
From: Jens Axboe <>
To: Yinyin Zhu <>,
Subject: Re: [PATCH] io_uring: fix the bug of child process can't do io task
Date: Tue, 15 Sep 2020 07:36:54 -0600	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 9/15/20 7:25 AM, Jens Axboe wrote:
> On 9/15/20 7:02 AM, Yinyin Zhu wrote:
>> when parent process setup a io_uring_instance, the ctx->sqo_mm was
>> assigned of parent process'mm. Then it fork a child
>> process. So the child process inherits the io_uring_instance fd from
>> parent process. Then the child process submit a io task to the io_uring
>> instance. The kworker will do the io task actually, and use
>> the ctx->sqo_mm as its mm, but this ctx->sqo_mm is parent process's mm,
>> not the child process's mm. so child do the io task unsuccessfully. To
>> fix this bug, when a process submit a io task to the kworker, assign the
>> ctx->sqo_mm with this process's mm.
> Hmm, what's the test case for this? There's a 5.9 regression where we
> don't always grab the right context for certain linked cases, below
> is the fix. Does that fix your case?

Ah hang on, you're on the 5.4 code base... I think this is a better
approach. Any chance you can test it?

The problem with yours is that you can have multiple pending async
ones, and you can't just re-assign ctx->sqo_mm. That one should only
be used by the SQPOLL thread.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2a539b794f3b..e8a4b4ae7006 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -514,7 +514,7 @@ static inline void io_queue_async_work(struct io_ring_ctx *ctx,
-	req->task = current;
+	req->task = get_task_struct(current);
 	spin_lock_irqsave(&ctx->task_lock, flags);
 	list_add(&req->task_list, &ctx->task_list);
@@ -1832,6 +1832,7 @@ static void io_poll_complete_work(struct work_struct *work)
+	put_task_struct(req->task);
@@ -2234,11 +2235,11 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 		ret = 0;
 		if (io_req_needs_user(req) && !cur_mm) {
-			if (!mmget_not_zero(ctx->sqo_mm)) {
+			if (!mmget_not_zero(req->task->mm)) {
 				ret = -EFAULT;
 				goto end_req;
 			} else {
-				cur_mm = ctx->sqo_mm;
+				cur_mm = req->task->mm;
 				old_fs = get_fs();
@@ -2275,6 +2276,7 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 		/* drop submission reference */
+		put_task_struct(req->task);
 		if (ret) {

Jens Axboe

  reply	other threads:[~2020-09-16  0:29 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 13:02 Yinyin Zhu
2020-09-15 13:25 ` Jens Axboe
2020-09-15 13:36   ` Jens Axboe [this message]
2020-09-16  3:53     ` [External] " 朱寅寅

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \
    --subject='Re: [PATCH] io_uring: fix the bug of child process can'\''t do io task' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).