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Date: Fri, 22 Mar 2019 12:14:00 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Jan Kara <jack@...e.cz>, Michal Hocko <mhocko@...e.com>, Andrew Morton <akpm@...ux-foundation.org>, Al Viro <viro@...IV.linux.org.uk>, Linus Torvalds <torvalds@...ux-foundation.org>, Sasha Levin <sashal@...nel.org> Subject: [PATCH 4.4 102/230] fs/drop_caches.c: avoid softlockups in drop_pagecache_sb() 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ [ 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@...e.cz> Acked-by: Michal Hocko <mhocko@...e.com> Reviewed-by: Andrew Morton <akpm@...ux-foundation.org> Cc: Al Viro <viro@...IV.linux.org.uk> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org> Signed-off-by: Sasha Levin <sashal@...nel.org> --- fs/drop_caches.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/fs/drop_caches.c b/fs/drop_caches.c index d72d52b90433..280460fef066 100644 --- a/fs/drop_caches.c +++ b/fs/drop_caches.c @@ -20,8 +20,13 @@ 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; } @@ -29,6 +34,7 @@ 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; -- 2.19.1
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