From: Waiman Long <longman@xxxxxxxxxx> Subject: mm/vmalloc: Fix unlock order in s_stop() When multiple locks are acquired, they should be released in reverse order. For s_start() and s_stop() in mm/vmalloc.c, that is not the case. s_start: mutex_lock(&vmap_purge_lock); spin_lock(&vmap_area_lock); s_stop : mutex_unlock(&vmap_purge_lock); spin_unlock(&vmap_area_lock); This unlock sequence, though allowed, is not optimal. If a waiter is present, mutex_unlock() will need to go through the slowpath of waking up the waiter with preemption disabled. Fix that by releasing the spinlock first before the mutex. Link: https://lkml.kernel.org/r/20201213180843.16938-1-longman@xxxxxxxxxx Fixes: e36176be1c39 ("mm/vmalloc: rework vmap_area_lock") Signed-off-by: Waiman Long <longman@xxxxxxxxxx> Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmalloc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/vmalloc.c~mm-vmalloc-fix-unlock-order-in-s_stop +++ a/mm/vmalloc.c @@ -3465,11 +3465,11 @@ static void *s_next(struct seq_file *m, } static void s_stop(struct seq_file *m, void *p) - __releases(&vmap_purge_lock) __releases(&vmap_area_lock) + __releases(&vmap_purge_lock) { - mutex_unlock(&vmap_purge_lock); spin_unlock(&vmap_area_lock); + mutex_unlock(&vmap_purge_lock); } static void show_numa_info(struct seq_file *m, struct vm_struct *v) _
