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Message-ID: <20110901052702.GA11856@zhy>
Date: Thu, 1 Sep 2011 13:27:02 +0800
From: Yong Zhang <yong.zhang0@...il.com>
To: Shan Hai <haishan.bai@...il.com>
Cc: akpm@...ux-foundation.org, tglx@...utronix.de,
eric.dumazet@...il.com, vapier@...too.org, asharma@...com,
linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH V2 1/1] lib/atomic64 using
raw_spin_lock_irq[save|resotre] for atomicity
On Thu, Sep 01, 2011 at 11:32:03AM +0800, Shan Hai wrote:
> The spin_lock_irq[save|restore] could break the atomicity of the
> atomic64_* operations in the PREEMPT-RT configuration, because
> the spin_lock_irq[save|restore] themselves are preemptable in the
> PREEMPT-RT, using raw variant of the spin lock could provide the
> atomicity that atomic64_* need.
>
> spin_lock_irq[save|restore] would cause the following OOPS on 2.6.34.9+rt
>
> OOPS on 2.6.34.9+PREEMPT-RT:
> ------------[ cut here ]------------
> kernel BUG at /build/linux/kernel/rtmutex.c:832!
> Oops: Exception in kernel mode, sig: 5 [#2]
> PREEMPT SMP NR_CPUS=8 LTT NESTING LEVEL : 0
> P4080 DS
> last sysfs file: /sys/devices/system/cpu/online
> Modules linked in: ipv6(+) [last unloaded: scsi_wait_scan]
> NIP: c068b218 LR: c068b1e0 CTR: 00000000
> REGS: eb459ae0 TRAP: 0700 Tainted: G D (2.6.34.9-rt)
> MSR: 00021002 <ME,CE> CR: 28000488 XER: 00000000
> TASK = ea43d3b0[968] 'perf' THREAD: eb458000 CPU: 0
> GPR00: 00000001 eb459b90 ea43d3b0 00021002 00000000 00000000 00000000 00000001
> GPR08: 00000001 ea43d3b0 c068b1e0 00000000 28000482 10092c4c 7fffffff 80000000
> GPR16: eb459d40 eb459c68 00000001 c2fa2098 eb459ec0 eac5a8e8 eac5a900 c0906308
> GPR24: c0906334 00000000 eb459b9c c090d0ec 00021002 c09062e0 c09062e0 eb459b90
> NIP [c068b218] rt_spin_lock_slowlock+0x78/0x3a8
> LR [c068b1e0] rt_spin_lock_slowlock+0x40/0x3a8
> Call Trace:
> [eb459b90] [c068b1e0] rt_spin_lock_slowlock+0x40/0x3a8 (unreliable)
> [eb459c20] [c068bdb0] rt_spin_lock+0x40/0x98
> [eb459c40] [c03d2a14] atomic64_read+0x48/0x84
> [eb459c60] [c001aaf4] perf_event_interrupt+0xec/0x28c
> [eb459d10] [c0010138] performance_monitor_exception+0x7c/0x150
> [eb459d30] [c0014170] ret_from_except_full+0x0/0x4c
> --- Exception: 2060 at lock_acquire+0x94/0x130
> LR = lock_acquire+0x8c/0x130
> [eb459e30] [c068bdf0] rt_spin_lock+0x80/0x98
> [eb459e50] [c03d2884] atomic64_add_return+0x50/0x98
> [eb459e70] [c00ff888] T.902+0x150/0x4f8
> [eb459eb0] [c00ffedc] sys_perf_event_open+0x2ac/0x508
> [eb459f40] [c0013b6c] ret_from_syscall+0x0/0x4
> --- Exception: c00 at 0xfa8abe4
> LR = 0x10016034
>
> Signed-off-by: Shan Hai <haishan.bai@...il.com>
Reviewed-by: Yong Zhang <yong.zhang0@...il.com>
> ---
> lib/atomic64.c | 44 ++++++++++++++++++++++----------------------
> 1 files changed, 22 insertions(+), 22 deletions(-)
>
> diff --git a/lib/atomic64.c b/lib/atomic64.c
> index e12ae0d..82b3313 100644
> --- a/lib/atomic64.c
> +++ b/lib/atomic64.c
> @@ -29,7 +29,7 @@
> * Ensure each lock is in a separate cacheline.
> */
> static union {
> - spinlock_t lock;
> + raw_spinlock_t lock;
> char pad[L1_CACHE_BYTES];
> } atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
>
> @@ -48,9 +48,9 @@ long long atomic64_read(const atomic64_t *v)
> spinlock_t *lock = lock_addr(v);
> long long val;
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> val = v->counter;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> return val;
> }
> EXPORT_SYMBOL(atomic64_read);
> @@ -60,9 +60,9 @@ void atomic64_set(atomic64_t *v, long long i)
> unsigned long flags;
> spinlock_t *lock = lock_addr(v);
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> v->counter = i;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> }
> EXPORT_SYMBOL(atomic64_set);
>
> @@ -71,9 +71,9 @@ void atomic64_add(long long a, atomic64_t *v)
> unsigned long flags;
> spinlock_t *lock = lock_addr(v);
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> v->counter += a;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> }
> EXPORT_SYMBOL(atomic64_add);
>
> @@ -83,9 +83,9 @@ long long atomic64_add_return(long long a, atomic64_t *v)
> spinlock_t *lock = lock_addr(v);
> long long val;
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> val = v->counter += a;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> return val;
> }
> EXPORT_SYMBOL(atomic64_add_return);
> @@ -95,9 +95,9 @@ void atomic64_sub(long long a, atomic64_t *v)
> unsigned long flags;
> spinlock_t *lock = lock_addr(v);
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> v->counter -= a;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> }
> EXPORT_SYMBOL(atomic64_sub);
>
> @@ -107,9 +107,9 @@ long long atomic64_sub_return(long long a, atomic64_t *v)
> spinlock_t *lock = lock_addr(v);
> long long val;
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> val = v->counter -= a;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> return val;
> }
> EXPORT_SYMBOL(atomic64_sub_return);
> @@ -120,11 +120,11 @@ long long atomic64_dec_if_positive(atomic64_t *v)
> spinlock_t *lock = lock_addr(v);
> long long val;
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> val = v->counter - 1;
> if (val >= 0)
> v->counter = val;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> return val;
> }
> EXPORT_SYMBOL(atomic64_dec_if_positive);
> @@ -135,11 +135,11 @@ long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
> spinlock_t *lock = lock_addr(v);
> long long val;
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> val = v->counter;
> if (val == o)
> v->counter = n;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> return val;
> }
> EXPORT_SYMBOL(atomic64_cmpxchg);
> @@ -150,10 +150,10 @@ long long atomic64_xchg(atomic64_t *v, long long new)
> spinlock_t *lock = lock_addr(v);
> long long val;
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> val = v->counter;
> v->counter = new;
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> return val;
> }
> EXPORT_SYMBOL(atomic64_xchg);
> @@ -164,12 +164,12 @@ int atomic64_add_unless(atomic64_t *v, long long a, long long u)
> spinlock_t *lock = lock_addr(v);
> int ret = 0;
>
> - spin_lock_irqsave(lock, flags);
> + raw_spin_lock_irqsave(lock, flags);
> if (v->counter != u) {
> v->counter += a;
> ret = 1;
> }
> - spin_unlock_irqrestore(lock, flags);
> + raw_spin_unlock_irqrestore(lock, flags);
> return ret;
> }
> EXPORT_SYMBOL(atomic64_add_unless);
> @@ -179,7 +179,7 @@ static int init_atomic64_lock(void)
> int i;
>
> for (i = 0; i < NR_LOCKS; ++i)
> - spin_lock_init(&atomic64_lock[i].lock);
> + raw_spin_lock_init(&atomic64_lock[i].lock);
> return 0;
> }
>
> --
> 1.7.4.1
>
> --
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