Re: [regression] fsnotify fails stress test since fsnotify_for_v5.15-rc1 merged

[Petr Vorel <pvorel@suse.cz>]

> On Tue, Sep 7, 2021 at 9:33 AM Murphy Zhou <jencce.kernel@gmail.com> wrote:

> > Hi,

> > Since this commit:

> > commit ec44610fe2b86daef70f3f53f47d2a2542d7094f
> > Author: Amir Goldstein <amir73il@gmail.com>
> > Date:   Tue Aug 10 18:12:19 2021 +0300

> >     fsnotify: count all objects with attached connectors




> > Kernel fsnotify can't finish a stress testcase that used to pass quickly.

> > Kernel hung at umount. Can not be killed but restarting the server.

> > Reproducer text is attached.


> Hi Murphy,

> Thank you for the detailed report.
> I was able to reproduce the hang and the attached patch fixes it for me.
> Cloud you please verify the fix yourself as well?

> This is a good regression test.
> Did you consider contributing it to LTP?
> I think the LTP team could also help converting your reproducer to
> an LTP test (CC: Petr).

@Murphy: yes, please contribute that to LTP. There are already fanotify tests [1],
here is the C API [2] and shell API [3] (if needed, it should be enough to write
it just in C). If you have any questions, don't hesitate ask on LTP ML and Cc
me.

@Amir: thanks!

Kind regards,
Petr

[1] https://github.com/linux-test-project/ltp/tree/master/testcases/kernel/syscalls/fanotify/
[2] https://github.com/linux-test-project/ltp/wiki/C-Test-API
[3] https://github.com/linux-test-project/ltp/wiki/Shell-Test-API

> Thanks,
> Amir.

> From 14d3c313062dfbc86b3d2c4d7deec56a096432f7 Mon Sep 17 00:00:00 2001
> From: Amir Goldstein <amir73il@gmail.com>
> Date: Thu, 9 Sep 2021 13:46:34 +0300
> Subject: [PATCH] fsnotify: fix sb_connectors leak

> Fix a leak in s_fsnotify_connectors counter in case of a race between
> concurrent add of new fsnotify mark to an object.

> The task that lost the race fails to drop the counter before freeing
> the unused connector.

> Fixes: ec44610fe2b8 ("fsnotify: count all objects with attached connectors")
> Reported-by: Murphy Zhou <jencce.kernel@gmail.com>
> Link: https://lore.kernel.org/linux-fsdevel/20210907063338.ycaw6wvhzrfsfdlp@xzhoux.usersys.redhat.com/
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/notify/mark.c | 1 +
>  1 file changed, 1 insertion(+)

> diff --git a/fs/notify/mark.c b/fs/notify/mark.c
> index 95006d1d29ab..fa1d99101f89 100644
> --- a/fs/notify/mark.c
> +++ b/fs/notify/mark.c
> @@ -531,6 +531,7 @@ static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
>  		/* Someone else created list structure for us */
>  		if (inode)
>  			fsnotify_put_inode_ref(inode);
> +		fsnotify_put_sb_connectors(conn);
>  		kmem_cache_free(fsnotify_mark_connector_cachep, conn);
>  	}