提交 57439f87 编写于 作者: N npiggin@suse.de 提交者: Linus Torvalds

fs: fix superblock iteration race

list_for_each_entry_safe is not suitable to protect against concurrent
modification of the list. 6754af64 introduced a race in sb walking.

list_for_each_entry can use the trick of pinning the current entry in
the list before we drop and retake the lock because it subsequently
follows cur->next. However list_for_each_entry_safe saves n=cur->next
for following before entering the loop body, so when the lock is
dropped, n may be deleted.
Signed-off-by: NNick Piggin <npiggin@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Frank Mayhar <fmayhar@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
上级 5904b3b8
...@@ -590,6 +590,8 @@ static void prune_dcache(int count) ...@@ -590,6 +590,8 @@ static void prune_dcache(int count)
up_read(&sb->s_umount); up_read(&sb->s_umount);
} }
spin_lock(&sb_lock); spin_lock(&sb_lock);
/* lock was dropped, must reset next */
list_safe_reset_next(sb, n, s_list);
count -= pruned; count -= pruned;
__put_super(sb); __put_super(sb);
/* more work left to do? */ /* more work left to do? */
......
...@@ -374,6 +374,8 @@ void sync_supers(void) ...@@ -374,6 +374,8 @@ void sync_supers(void)
up_read(&sb->s_umount); up_read(&sb->s_umount);
spin_lock(&sb_lock); spin_lock(&sb_lock);
/* lock was dropped, must reset next */
list_safe_reset_next(sb, n, s_list);
__put_super(sb); __put_super(sb);
} }
} }
...@@ -405,6 +407,8 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg) ...@@ -405,6 +407,8 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
up_read(&sb->s_umount); up_read(&sb->s_umount);
spin_lock(&sb_lock); spin_lock(&sb_lock);
/* lock was dropped, must reset next */
list_safe_reset_next(sb, n, s_list);
__put_super(sb); __put_super(sb);
} }
spin_unlock(&sb_lock); spin_unlock(&sb_lock);
...@@ -585,6 +589,8 @@ static void do_emergency_remount(struct work_struct *work) ...@@ -585,6 +589,8 @@ static void do_emergency_remount(struct work_struct *work)
} }
up_write(&sb->s_umount); up_write(&sb->s_umount);
spin_lock(&sb_lock); spin_lock(&sb_lock);
/* lock was dropped, must reset next */
list_safe_reset_next(sb, n, s_list);
__put_super(sb); __put_super(sb);
} }
spin_unlock(&sb_lock); spin_unlock(&sb_lock);
......
...@@ -544,6 +544,21 @@ static inline void list_splice_tail_init(struct list_head *list, ...@@ -544,6 +544,21 @@ static inline void list_splice_tail_init(struct list_head *list,
&pos->member != (head); \ &pos->member != (head); \
pos = n, n = list_entry(n->member.prev, typeof(*n), member)) pos = n, n = list_entry(n->member.prev, typeof(*n), member))
/**
* list_safe_reset_next - reset a stale list_for_each_entry_safe loop
* @pos: the loop cursor used in the list_for_each_entry_safe loop
* @n: temporary storage used in list_for_each_entry_safe
* @member: the name of the list_struct within the struct.
*
* list_safe_reset_next is not safe to use in general if the list may be
* modified concurrently (eg. the lock is dropped in the loop body). An
* exception to this is if the cursor element (pos) is pinned in the list,
* and list_safe_reset_next is called after re-taking the lock and before
* completing the current iteration of the loop body.
*/
#define list_safe_reset_next(pos, n, member) \
n = list_entry(pos->member.next, typeof(*pos), member)
/* /*
* Double linked lists with a single pointer list head. * Double linked lists with a single pointer list head.
* Mostly useful for hash tables where the two pointer list head is * Mostly useful for hash tables where the two pointer list head is
......
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