3.2.94-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Sahitya Tummala <stummala@xxxxxxxxxxxxxx> commit b17c070fb624cf10162cf92ea5e1ec25cd8ac176 upstream. __list_lru_walk_one() acquires nlru spin lock (nlru->lock) for longer duration if there are more number of items in the lru list. As per the current code, it can hold the spin lock for upto maximum UINT_MAX entries at a time. So if there are more number of items in the lru list, then "BUG: spinlock lockup suspected" is observed in the below path: spin_bug+0x90 do_raw_spin_lock+0xfc _raw_spin_lock+0x28 list_lru_add+0x28 dput+0x1c8 path_put+0x20 terminate_walk+0x3c path_lookupat+0x100 filename_lookup+0x6c user_path_at_empty+0x54 SyS_faccessat+0xd0 el0_svc_naked+0x24 This nlru->lock is acquired by another CPU in this path - d_lru_shrink_move+0x34 dentry_lru_isolate_shrink+0x48 __list_lru_walk_one.isra.10+0x94 list_lru_walk_node+0x40 shrink_dcache_sb+0x60 do_remount_sb+0xbc do_emergency_remount+0xb0 process_one_work+0x228 worker_thread+0x2e0 kthread+0xf4 ret_from_fork+0x10 Fix this lockup by reducing the number of entries to be shrinked from the lru list to 1024 at once. Also, add cond_resched() before processing the lru list again. Link: http://marc.info/?t=149722864900001&r=1&w=2 Link: http://lkml.kernel.org/r/1498707575-2472-1-git-send-email-stummala@xxxxxxxxxxxxxx Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx> Suggested-by: Jan Kara <jack@xxxxxxx> Suggested-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Acked-by: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: Alexander Polakov <apolyakov@xxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> [bwh: Backported to 3.2: we don't hold the spin-lock for long, but adding cond_resched() looks like a good idea] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- fs/dcache.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -836,6 +836,7 @@ void shrink_dcache_sb(struct super_block list_splice_init(&sb->s_dentry_lru, &tmp); spin_unlock(&dcache_lru_lock); shrink_dentry_list(&tmp); + cond_resched(); spin_lock(&dcache_lru_lock); } spin_unlock(&dcache_lru_lock);