linux-kernel - [PATCH] fs/dcache.c: re-add cond_resched() in shrink_dcache

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Date:   Fri, 13 Apr 2018 13:28:23 -0700
From:   Khazhismel Kumykov <khazhy@...gle.com>
To:     nborisov@...e.com, akpm@...ux-foundation.org
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Khazhismel Kumykov <khazhy@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Jeff Mahoney <jeffm@...e.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] fs/dcache.c: re-add cond_resched() in shrink_dcache_parent()

shrink_dcache_parent may spin waiting for a parallel shrink_dentry_list.
In this case we may have 0 dentries to dispose, so we will never
schedule out while waiting for the parallel shrink_dentry_list to
complete.

Tested that this fixes syzbot reports of stalls in shrink_dcache_parent()

Fixes: 32785c0539b7 ("fs/dcache.c: add cond_resched() in shrink_dentry_list()")
Reported-by: syzbot+ae80b790eb412884ca77@...kaller.appspotmail.com

Cc: Nikolay Borisov <nborisov@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>
Cc: Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc: Jeff Mahoney <jeffm@...e.com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>
---
 fs/dcache.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 591b34500e41..3507badeb60a 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1489,6 +1489,7 @@ void shrink_dcache_parent(struct dentry *parent)
 			break;
 
 		shrink_dentry_list(&data.dispose);
+		cond_resched();
 	}
 }
 EXPORT_SYMBOL(shrink_dcache_parent);
-- 
2.17.0.484.g0c8726318c-goog


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