From: Sahitya Tummala <stummala@xxxxxxxxxxxxxx> Subject: fs/dcache.c: fix spin lockup issue on nlru->lock __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 - [<ffffff8eca0fb0bc>] spin_bug+0x90 [<ffffff8eca0fb220>] do_raw_spin_lock+0xfc [<ffffff8ecafb7798>] _raw_spin_lock+0x28 [<ffffff8eca1ae884>] list_lru_add+0x28 [<ffffff8eca1f5dac>] dput+0x1c8 [<ffffff8eca1eb46c>] path_put+0x20 [<ffffff8eca1eb73c>] terminate_walk+0x3c [<ffffff8eca1eee58>] path_lookupat+0x100 [<ffffff8eca1f00fc>] filename_lookup+0x6c [<ffffff8eca1f0264>] user_path_at_empty+0x54 [<ffffff8eca1e066c>] SyS_faccessat+0xd0 [<ffffff8eca084e30>] el0_svc_naked+0x24 This nlru->lock is acquired by another CPU in this path - [<ffffff8eca1f5fd0>] d_lru_shrink_move+0x34 [<ffffff8eca1f6180>] dentry_lru_isolate_shrink+0x48 [<ffffff8eca1aeafc>] __list_lru_walk_one.isra.10+0x94 [<ffffff8eca1aec34>] list_lru_walk_node+0x40 [<ffffff8eca1f6620>] shrink_dcache_sb+0x60 [<ffffff8eca1e56a8>] do_remount_sb+0xbc [<ffffff8eca1e583c>] do_emergency_remount+0xb0 [<ffffff8eca0ba510>] process_one_work+0x228 [<ffffff8eca0bb158>] worker_thread+0x2e0 [<ffffff8eca0c040c>] kthread+0xf4 [<ffffff8eca084dd0>] 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> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/dcache.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff -puN fs/dcache.c~fs-dcachec-fix-spin-lockup-issue-on-nlru-lock fs/dcache.c --- a/fs/dcache.c~fs-dcachec-fix-spin-lockup-issue-on-nlru-lock +++ a/fs/dcache.c @@ -1160,11 +1160,12 @@ void shrink_dcache_sb(struct super_block LIST_HEAD(dispose); freed = list_lru_walk(&sb->s_dentry_lru, - dentry_lru_isolate_shrink, &dispose, UINT_MAX); + dentry_lru_isolate_shrink, &dispose, 1024); this_cpu_sub(nr_dentry_unused, freed); shrink_dentry_list(&dispose); - } while (freed > 0); + cond_resched(); + } while (list_lru_count(&sb->s_dentry_lru) > 0); } EXPORT_SYMBOL(shrink_dcache_sb); _