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

[Khazhismel Kumykov]

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@xxxxxxxxxxxxxxxxxxxxxxxxx

Cc: Nikolay Borisov <nborisov@xxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Goldwyn Rodrigues <rgoldwyn@xxxxxxx>
Cc: Jeff Mahoney <jeffm@xxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx>
---
 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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