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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Will Deacon <will.deacon@arm.com>, Peter Zijlstra <peterz@infradead.org>
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"mingo@kernel.org" <mingo@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"linux-snps-arc@lists.infradead.org" 
	<linux-snps-arc@lists.infradead.org>,
	Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
	"yamada.masahiro@socionext.com" <yamada.masahiro@socionext.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash
Date: Fri, 31 Aug 2018 00:42:46 +0000	[thread overview]
Message-ID: <C2D7FE5348E1B147BCA15975FBA23075012B091016@us01wembx1.internal.synopsys.com> (raw)
In-Reply-To: 20180830095148.GB5942@arm.com

On 08/30/2018 02:51 AM, Will Deacon wrote:
> Yeah, the bit_spin_lock()/__bit_spin_unlock() race described in f75d48644c56a
> boils down to concurrent atomic_long_set_release() vs
> atomic_long_fetch_or_acquire(), which really needs to work.

I don't see how: __clear_bit_unlock() reads @old, flips a bit and then calls
atomic_long_set_release() so the race is not just with set_release.

    static inline int test_and_set_bit_lock(unsigned int nr, volatile unsigned
long *p)
    {
      long old;
      unsigned long mask = (1UL << ((nr) % 32));

      p += ((nr) / 32);
      old = atomic_long_fetch_or_acquire(mask, (atomic_long_t *)p);
      return !!(old & mask);
    }

    static inline void __clear_bit_unlock(unsigned int nr, volatile unsigned long *p)
    {
       unsigned long old;

     p += ((nr) / 32);
    old = // soem typecheck magic on *p
    old &= ~(1UL << ((nr) % 32));
    atomic_long_set_release((atomic_long_t *)p, old);
  }

WARNING: multiple messages have this Message-ID (diff)
From: Vineet.Gupta1@synopsys.com (Vineet Gupta)
To: linux-snps-arc@lists.infradead.org
Subject: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash
Date: Fri, 31 Aug 2018 00:42:46 +0000	[thread overview]
Message-ID: <C2D7FE5348E1B147BCA15975FBA23075012B091016@us01wembx1.internal.synopsys.com> (raw)
In-Reply-To: 20180830095148.GB5942@arm.com

On 08/30/2018 02:51 AM, Will Deacon wrote:
> Yeah, the bit_spin_lock()/__bit_spin_unlock() race described in f75d48644c56a
> boils down to concurrent atomic_long_set_release() vs
> atomic_long_fetch_or_acquire(), which really needs to work.

I don't see how: __clear_bit_unlock() reads @old, flips a bit and then calls
atomic_long_set_release() so the race is not just with set_release.

    static inline int test_and_set_bit_lock(unsigned int nr, volatile unsigned
long *p)
    {
      long old;
      unsigned long mask = (1UL << ((nr) % 32));

      p += ((nr) / 32);
      old = atomic_long_fetch_or_acquire(mask, (atomic_long_t *)p);
      return !!(old & mask);
    }

    static inline void __clear_bit_unlock(unsigned int nr, volatile unsigned long *p)
    {
       unsigned long old;

     p += ((nr) / 32);
    old = // soem typecheck magic on *p
    old &= ~(1UL << ((nr) % 32));
    atomic_long_set_release((atomic_long_t *)p, old);
  }

WARNING: multiple messages have this Message-ID (diff)
From: Vineet.Gupta1@synopsys.com (Vineet Gupta)
To: linux-arm-kernel@lists.infradead.org
Subject: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash
Date: Fri, 31 Aug 2018 00:42:46 +0000	[thread overview]
Message-ID: <C2D7FE5348E1B147BCA15975FBA23075012B091016@us01wembx1.internal.synopsys.com> (raw)
In-Reply-To: 20180830095148.GB5942@arm.com

On 08/30/2018 02:51 AM, Will Deacon wrote:
> Yeah, the bit_spin_lock()/__bit_spin_unlock() race described in f75d48644c56a
> boils down to concurrent atomic_long_set_release() vs
> atomic_long_fetch_or_acquire(), which really needs to work.

I don't see how: __clear_bit_unlock() reads @old, flips a bit and then calls
atomic_long_set_release() so the race is not just with set_release.

    static inline int test_and_set_bit_lock(unsigned int nr, volatile unsigned
long *p)
    {
      long old;
      unsigned long mask = (1UL << ((nr) % 32));

      p += ((nr) / 32);
      old = atomic_long_fetch_or_acquire(mask, (atomic_long_t *)p);
      return !!(old & mask);
    }

    static inline void __clear_bit_unlock(unsigned int nr, volatile unsigned long *p)
    {
       unsigned long old;

     p += ((nr) / 32);
    old = // soem typecheck magic on *p
    old &= ~(1UL << ((nr) % 32));
    atomic_long_set_release((atomic_long_t *)p, old);
  }

  parent reply	other threads:[~2018-08-31  0:42 UTC|newest]

Thread overview: 89+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-29 18:33 Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash Eugeniy Paltsev
2018-08-29 18:33 ` Eugeniy Paltsev
2018-08-29 18:33 ` Eugeniy Paltsev
2018-08-29 18:33 ` Eugeniy Paltsev
2018-08-29 21:16 ` Vineet Gupta
2018-08-29 21:16   ` Vineet Gupta
2018-08-29 21:16   ` Vineet Gupta
2018-08-29 21:16   ` Vineet Gupta
2018-08-30  9:35   ` Will Deacon
2018-08-30  9:35     ` Will Deacon
2018-08-30  9:35     ` Will Deacon
2018-08-30  9:35     ` Will Deacon
2018-08-30  9:44   ` Peter Zijlstra
2018-08-30  9:44     ` Peter Zijlstra
2018-08-30  9:44     ` Peter Zijlstra
2018-08-30  9:44     ` Peter Zijlstra
2018-08-30  9:44     ` Peter Zijlstra
2018-08-30  9:51     ` Will Deacon
2018-08-30  9:51       ` Will Deacon
2018-08-30  9:51       ` Will Deacon
2018-08-30  9:51       ` Will Deacon
2018-08-30 11:53       ` Eugeniy Paltsev
2018-08-30 11:53         ` Eugeniy Paltsev
2018-08-30 11:53         ` Eugeniy Paltsev
2018-08-30 11:53         ` Eugeniy Paltsev
2018-08-30 13:57         ` Will Deacon
2018-08-30 13:57           ` Will Deacon
2018-08-30 13:57           ` Will Deacon
2018-08-30 13:57           ` Will Deacon
2018-08-30 14:17         ` Peter Zijlstra
2018-08-30 14:17           ` Peter Zijlstra
2018-08-30 14:17           ` Peter Zijlstra
2018-08-30 14:17           ` Peter Zijlstra
2018-08-30 14:17           ` Peter Zijlstra
2018-08-30 14:23           ` Will Deacon
2018-08-30 14:23             ` Will Deacon
2018-08-30 14:23             ` Will Deacon
2018-08-30 14:23             ` Will Deacon
2018-08-30 14:29             ` Peter Zijlstra
2018-08-30 14:29               ` Peter Zijlstra
2018-08-30 14:29               ` Peter Zijlstra
2018-08-30 14:29               ` Peter Zijlstra
2018-08-30 14:43               ` Peter Zijlstra
2018-08-30 14:43                 ` Peter Zijlstra
2018-08-30 14:43                 ` Peter Zijlstra
2018-08-30 14:43                 ` Peter Zijlstra
2018-08-30 14:43                 ` Peter Zijlstra
2020-04-14  1:19                 ` Vineet Gupta
2020-04-14  1:19                   ` Vineet Gupta
2020-04-14  1:19                   ` Vineet Gupta
2020-04-14  1:19                   ` Vineet Gupta
2018-08-30 20:31               ` Vineet Gupta
2018-08-30 20:31                 ` Vineet Gupta
2018-08-30 20:31                 ` Vineet Gupta
2018-08-30 20:31                 ` Vineet Gupta
2018-08-30 20:45                 ` Peter Zijlstra
2018-08-30 20:45                   ` Peter Zijlstra
2018-08-30 20:45                   ` Peter Zijlstra
2018-08-30 20:45                   ` Peter Zijlstra
2018-08-30 20:45                   ` Peter Zijlstra
2018-08-31  0:30                   ` Vineet Gupta
2018-08-31  0:30                     ` Vineet Gupta
2018-08-31  0:30                     ` Vineet Gupta
2018-08-31  0:30                     ` Vineet Gupta
2018-08-31  9:53                     ` Will Deacon
2018-08-31  9:53                       ` Will Deacon
2018-08-31  9:53                       ` Will Deacon
2018-08-31  9:53                       ` Will Deacon
2018-08-30 14:46           ` Eugeniy Paltsev
2018-08-30 14:46             ` Eugeniy Paltsev
2018-08-30 14:46             ` Eugeniy Paltsev
2018-08-30 14:46             ` Eugeniy Paltsev
2018-08-30 14:46             ` Eugeniy Paltsev
2018-08-30 17:15             ` Peter Zijlstra
2018-08-30 17:15               ` Peter Zijlstra
2018-08-30 17:15               ` Peter Zijlstra
2018-08-30 17:15               ` Peter Zijlstra
2018-08-31  0:42       ` Vineet Gupta [this message]
2018-08-31  0:42         ` Vineet Gupta
2018-08-31  0:42         ` Vineet Gupta
2018-08-31  0:42         ` Vineet Gupta
2018-08-31  0:29     ` __clear_bit_lock to use atomic clear_bit (was Re: Patch "asm-generic/bitops/lock.h) Vineet Gupta
2018-08-31  0:29       ` Vineet Gupta
2018-08-31  0:29       ` Vineet Gupta
2018-08-31  0:29       ` Vineet Gupta
2018-08-31  7:24       ` Peter Zijlstra
2018-08-31  7:24         ` Peter Zijlstra
2018-08-31  7:24         ` Peter Zijlstra
2018-08-31  7:24         ` Peter Zijlstra

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