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mm/vmalloc: Fix unlock order in s_stop()

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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@redhat.com
Fixes: e36176be1c39 ("mm/vmalloc: rework vmap_area_lock")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Waiman Long 2020-12-14 19:08:59 -08:00 committed by Linus Torvalds
parent e924d461f2
commit 0a7dd4e901
1 changed files with 2 additions and 2 deletions
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4
mm/vmalloc.c
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@ -3465,11 +3465,11 @@ static void *s_next(struct seq_file *m, void *p, loff_t *pos)
}
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)