Commit 5a817641 authored May 15, 2018 by Waiman Long Committed by Ingo Molnar May 16, 2018

locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN



The filesystem freezing code needs to transfer ownership of a rwsem
embedded in a percpu-rwsem from the task that does the freezing to
another one that does the thawing by calling percpu_rwsem_release()
after freezing and percpu_rwsem_acquire() before thawing.

However, the new rwsem debug code runs afoul with this scheme by warning
that the task that releases the rwsem isn't the one that acquires it,
as reported by Amir Goldstein:

  DEBUG_LOCKS_WARN_ON(sem->owner != get_current())
  WARNING: CPU: 1 PID: 1401 at /home/amir/build/src/linux/kernel/locking/rwsem.c:133 up_write+0x59/0x79

  Call Trace:
   percpu_up_write+0x1f/0x28
   thaw_super_locked+0xdf/0x120
   do_vfs_ioctl+0x270/0x5f1
   ksys_ioctl+0x52/0x71
   __x64_sys_ioctl+0x16/0x19
   do_syscall_64+0x5d/0x167
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

To work properly with the rwsem debug code, we need to annotate that the
rwsem ownership is unknown during the tranfer period until a brave soul
comes forward to acquire the ownership. During that period, optimistic
spinning will be disabled.

Reported-by: Amir Goldstein <amir73il@gmail.com>
Tested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-fsdevel@vger.kernel.org
Link: http://lkml.kernel.org/r/1526420991-21213-3-git-send-email-longman@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent d7d760ef

include/linux/percpu-rwsem.h

+5 −1

Original line number	Diff line number	Diff line
		@@ -133,7 +133,7 @@ static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
		lock_release(&sem->rw_sem.dep_map, 1, ip);
		#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
		if (!read)
		sem->rw_sem.owner = NULL;
		sem->rw_sem.owner = RWSEM_OWNER_UNKNOWN;
		#endif
		}

		@@ -141,6 +141,10 @@ static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
		bool read, unsigned long ip)
		{
		lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
		#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
		if (!read)
		sem->rw_sem.owner = current;
		#endif
		}

		#endif

include/linux/rwsem.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -44,6 +44,12 @@ struct rw_semaphore {
		#endif
		};

		/*
		* Setting bit 0 of the owner field with other non-zero bits will indicate
		* that the rwsem is writer-owned with an unknown owner.
		*/
		#define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-1L)

		extern struct rw_semaphore rwsem_down_read_failed(struct rw_semaphore sem);
		extern struct rw_semaphore rwsem_down_read_failed_killable(struct rw_semaphore sem);
		extern struct rw_semaphore rwsem_down_write_failed(struct rw_semaphore sem);

kernel/locking/rwsem-xadd.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -352,6 +352,8 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
		struct task_struct *owner;
		bool ret = true;

		BUILD_BUG_ON(!rwsem_has_anonymous_owner(RWSEM_OWNER_UNKNOWN));

		if (need_resched())
		return false;

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