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>
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@ -21,8 +21,13 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
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spin_lock(&sb->s_inode_list_lock);
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list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
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spin_lock(&inode->i_lock);
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/*
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* We must skip inodes in unusual state. We may also skip
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* inodes without pages but we deliberately won't in case
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* we need to reschedule to avoid softlockups.
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*/
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if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
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(inode->i_mapping->nrpages == 0)) {
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(inode->i_mapping->nrpages == 0 && !need_resched())) {
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spin_unlock(&inode->i_lock);
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continue;
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}
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@ -30,6 +35,7 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
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spin_unlock(&inode->i_lock);
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spin_unlock(&sb->s_inode_list_lock);
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cond_resched();
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invalidate_mapping_pages(inode->i_mapping, 0, -1);
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iput(toput_inode);
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toput_inode = inode;
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