diff mbox series

[5.10,453/717] mm/vmalloc: Fix unlock order in s_stop()

Message ID 20201228125042.672572617@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman Dec. 28, 2020, 12:47 p.m. UTC 
From: Waiman Long <longman@redhat.com>

[ Upstream commit 0a7dd4e901b8a4ee040ba953900d1d7120b34ee5 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/vmalloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
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Patch

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 6ae491a8b210f..75913f685c71e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3448,11 +3448,11 @@  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)