Commit c27d82f5 authored Feb 01, 2019 by Jan Kara Committed by Linus Torvalds Feb 01, 2019

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

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>

parent e0a352fa

fs/drop_caches.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -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;

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