From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw0-f193.google.com ([209.85.161.193]:46862 "EHLO mail-yw0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751151AbeEPFh0 (ORCPT ); Wed, 16 May 2018 01:37:26 -0400 MIME-Version: 1.0 In-Reply-To: <1526420991-21213-3-git-send-email-longman@redhat.com> References: <1526420991-21213-1-git-send-email-longman@redhat.com> <1526420991-21213-3-git-send-email-longman@redhat.com> From: Amir Goldstein Date: Wed, 16 May 2018 08:37:24 +0300 Message-ID: Subject: Re: [PATCH v4 2/2] locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN To: Waiman Long Cc: Ingo Molnar , Peter Zijlstra , Thomas Gleixner , linux-kernel , linux-fsdevel , Davidlohr Bueso , "Theodore Y. Ts'o" , Oleg Nesterov , Jan Kara , Matthew Wilcox Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, May 16, 2018 at 12:49 AM, Waiman Long wrote: > 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. > > [ 20.302978] ------------[ cut here ]------------ > [ 20.305016] DEBUG_LOCKS_WARN_ON(sem->owner != get_current()) > [ 20.305029] WARNING: CPU: 1 PID: 1401 at > /home/amir/build/src/linux/kernel/locking/rwsem.c:133 up_write+0x59/0x79 > [ 20.311252] CPU: 1 PID: 1401 Comm: fsfreeze Not tainted 4.17.0-rc3-xfstests-00049-g39e47bf59eb3 #3276 > [ 20.314808] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), > BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 > [ 20.318403] RIP: 0010:up_write+0x59/0x79 > [ 20.320928] RSP: 0018:ffffc90000717e48 EFLAGS: 00010286 > [ 20.322955] RAX: 0000000000000030 RBX: ffff880078f1c680 RCX: ffff880078e42200 > [ 20.325665] RDX: ffffffff810cc9c1 RSI: 0000000000000001 RDI: 0000000000000202 > [ 20.328844] RBP: ffffc90000717e80 R08: 0000000000000001 R09: 0000000000000001 > [ 20.332340] R10: ffffc90000717c58 R11: ffffffff836807ad R12: ffff880078f1c388 > [ 20.335095] R13: ffff880078a8b980 R14: 0000000000000000 R15: 00000000fffffff7 > [ 20.338009] FS: 00007fb61ca42700(0000) GS:ffff88007f400000(0000) knlGS:0000000000000000 > [ 20.341423] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 20.343772] CR2: 00007fb61c559b30 CR3: 0000000078da6000 CR4: 00000000000006e0 > [ 20.346463] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 20.349201] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 20.351960] Call Trace: > [ 20.352911] percpu_up_write+0x1f/0x28 > [ 20.354344] thaw_super_locked+0xdf/0x120 > [ 20.355944] do_vfs_ioctl+0x270/0x5f1 > [ 20.357390] ? __se_sys_newfstat+0x2e/0x39 > [ 20.358969] ? entry_SYSCALL_64_after_hwframe+0x59/0xbe > [ 20.360991] ksys_ioctl+0x52/0x71 > [ 20.362384] __x64_sys_ioctl+0x16/0x19 > [ 20.363702] do_syscall_64+0x5d/0x167 > [ 20.365099] 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. > > Signed-off-by: Waiman Long Looks good and tested Thanks, Amir. > --- > include/linux/percpu-rwsem.h | 6 +++++- > include/linux/rwsem.h | 6 ++++++ > kernel/locking/rwsem-xadd.c | 2 ++ > 3 files changed, 13 insertions(+), 1 deletion(-) > > diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h > index b1f37a8..79b99d6 100644 > --- a/include/linux/percpu-rwsem.h > +++ b/include/linux/percpu-rwsem.h > @@ -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 > diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h > index 56707d5..ab93b6e 100644 > --- 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); > diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c > index 604d247..a903367 100644 > --- a/kernel/locking/rwsem-xadd.c > +++ b/kernel/locking/rwsem-xadd.c > @@ -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; > > -- > 1.8.3.1 >