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fs/drop_caches.c: avoid softlockups in drop_pagecache_sb()

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[ Upstream commit c27d82f52f75fc9d8d9d40d120d2a96fdeeada5e ]

When superblock has lots of inodes without any pagecache (like is the
case for /proc), drop_pagecache_sb() will iterate through all of them
without dropping sb->s_inode_list_lock which can lead to softlockups
(one of our customers hit this).

Fix the problem by going to the slow path and doing cond_resched() in
case the process needs rescheduling.

Link: http://lkml.kernel.org/r/20190114085343.15011-1-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jan Kara 2019-02-01 14:21:23 -08:00 committed by Greg Kroah-Hartman
parent f1524fd049
commit 3d0acc076f
1 changed files with 7 additions and 1 deletions
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8
fs/drop_caches.c
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@ -21,8 +21,13 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
spin_lock(&sb->s_inode_list_lock);
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
spin_lock(&inode->i_lock);
/*
* We must skip inodes in unusual state. We may also skip
* inodes without pages but we deliberately won't in case
* we need to reschedule to avoid softlockups.
*/
if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
(inode->i_mapping->nrpages == 0)) {
(inode->i_mapping->nrpages == 0 && !need_resched())) {
spin_unlock(&inode->i_lock);
continue;
}
@ -30,6 +35,7 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
spin_unlock(&inode->i_lock);
spin_unlock(&sb->s_inode_list_lock);
cond_resched();
invalidate_mapping_pages(inode->i_mapping, 0, -1);
iput(toput_inode);
toput_inode = inode;