The patch titled
Subject: fs/drop_caches.c: avoid softlockups in drop_pagecache_sb()
has been added to the -mm tree. Its filename is
vfs-avoid-softlockups-in-drop_pagecache_sb.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/vfs-avoid-softlockups-in-drop_pagecache_sb.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/vfs-avoid-softlockups-in-drop_pagecache_sb.patch
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: 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@xxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/drop_caches.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/fs/drop_caches.c~vfs-avoid-softlockups-in-drop_pagecache_sb
+++ a/fs/drop_caches.c
@@ -21,8 +21,13 @@ static void drop_pagecache_sb(struct sup
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 sup
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;
_
Patches currently in -mm which might be from jack@xxxxxxx are
mm-migrate-make-buffer_migrate_page_norefs-actually-succeed.patch
vfs-avoid-softlockups-in-drop_pagecache_sb.patch
