Return-Path: Received: from mx2.suse.de ([195.135.220.15]:56114 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725898AbeLFQMA (ORCPT ); Thu, 6 Dec 2018 11:12:00 -0500 From: Jan Kara To: Al Viro Cc: , mhocko@suse.cz, Jan Kara Subject: [PATCH] vfs: Avoid softlockups in drop_pagecache_sb() Date: Thu, 6 Dec 2018 17:11:52 +0100 Message-Id: <20181206161152.3290-1-jack@suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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. Fix the problem by going to the slow path and doing cond_resched() in case the process needs rescheduling. Signed-off-by: Jan Kara --- 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 82377017130f..d31b6c72b476 100644 --- a/fs/drop_caches.c +++ b/fs/drop_caches.c @@ -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; -- 2.16.4