4.16-stable review patch. If anyone has any objections, please let me know.
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From: Waiman Long longman@redhat.com
[ Upstream commit 5a817641f68a6399a5fac8b7d2da67a73698ffed ]
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.co... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/percpu-rwsem.h | 6 +++++- include/linux/rwsem.h | 6 ++++++ kernel/locking/rwsem-xadd.c | 2 ++ 3 files changed, 13 insertions(+), 1 deletion(-)
--- a/include/linux/percpu-rwsem.h +++ b/include/linux/percpu-rwsem.h @@ -133,7 +133,7 @@ static inline void percpu_rwsem_release( 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( 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 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -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); --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -352,6 +352,8 @@ static inline bool rwsem_can_spin_on_own struct task_struct *owner; bool ret = true;
+ BUILD_BUG_ON(!rwsem_has_anonymous_owner(RWSEM_OWNER_UNKNOWN)); + if (need_resched()) return false;