On Thu, Sep 09, 2021 at 01:14:05PM +0200, Petr Vorel wrote:

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On Tue, Sep 7, 2021 at 9:33 AM Murphy Zhou [off-list ref] wrote:

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Hi,

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Since this commit:

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commit ec44610fe2b86daef70f3f53f47d2a2542d7094f
Author: Amir Goldstein [off-list ref]
Date:   Tue Aug 10 18:12:19 2021 +0300

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    fsnotify: count all objects with attached connectors

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

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

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Reproducer text is attached.

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Hi Murphy,

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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?

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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).

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@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.

I see you've contributed to LTP already :).

Ya :) Thank you for the links. That's very helpful!

Kind regards,
Petr

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@Amir: thanks!

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Kind regards,
Petr

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[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

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Thanks,
Amir.

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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

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

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

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

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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);
 	}

-- 
Murphy