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Revision 38d78e587d4960d0db94add518d27ee74bad2301 authored by Vladimir Davydov on 22 March 2013, 22:04:51 UTC, committed by Linus Torvalds on 22 March 2013, 23:41:21 UTC 
mqueue: sys_mq_open: do not call mnt_drop_write() if read-only
 
mnt_drop_write() must be called only if mnt_want_write() succeeded,
otherwise the mnt_writers counter will diverge.

mnt_writers counters are used to check if remounting FS as read-only is
OK, so after an extra mnt_drop_write() call, it would be impossible to
remount mqueue FS as read-only.  Besides, on umount a warning would be
printed like this one:

  =====================================
  [ BUG: bad unlock balance detected! ]
  3.9.0-rc3 #5 Not tainted
  -------------------------------------
  a.out/12486 is trying to release lock (sb_writers) at:
  mnt_drop_write+0x1f/0x30
  but there are no more locks to release!

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Doug Ledford <dledford@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent ca4b3f3
Raw File
mutex-debug.h 
/*
 * Mutexes: blocking mutual exclusion locks
 *
 * started by Ingo Molnar:
 *
 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 * This file contains mutex debugging related internal declarations,
 * prototypes and inline functions, for the CONFIG_DEBUG_MUTEXES case.
 * More details are in kernel/mutex-debug.c.
 */

/*
 * This must be called with lock->wait_lock held.
 */
extern void debug_mutex_lock_common(struct mutex *lock,
				    struct mutex_waiter *waiter);
extern void debug_mutex_wake_waiter(struct mutex *lock,
				    struct mutex_waiter *waiter);
extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
extern void debug_mutex_add_waiter(struct mutex *lock,
				   struct mutex_waiter *waiter,
				   struct thread_info *ti);
extern void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
				struct thread_info *ti);
extern void debug_mutex_unlock(struct mutex *lock);
extern void debug_mutex_init(struct mutex *lock, const char *name,
			     struct lock_class_key *key);

static inline void mutex_set_owner(struct mutex *lock)
{
	lock->owner = current;
}

static inline void mutex_clear_owner(struct mutex *lock)
{
	lock->owner = NULL;
}

#define spin_lock_mutex(lock, flags)			\
	do {						\
		struct mutex *l = container_of(lock, struct mutex, wait_lock); \
							\
		DEBUG_LOCKS_WARN_ON(in_interrupt());	\
		local_irq_save(flags);			\
		arch_spin_lock(&(lock)->rlock.raw_lock);\
		DEBUG_LOCKS_WARN_ON(l->magic != l);	\
	} while (0)

#define spin_unlock_mutex(lock, flags)				\
	do {							\
		arch_spin_unlock(&(lock)->rlock.raw_lock);	\
		local_irq_restore(flags);			\
		preempt_check_resched();			\
	} while (0)
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