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SubjectRe: [PATCH v4 2/2] locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN
On Wed, May 16, 2018 at 12:49 AM, Waiman Long <longman@redhat.com> 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 <longman@redhat.com>

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
>

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