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Groups > linux.kernel > #1188195
| From | "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() |
| Date | 2015-07-20 15:50 +0200 |
| Message-ID | <pOjCb-2OM-19@gated-at.bofh.it> (permalink) |
| References | (5 earlier) <pMT73-22W-15@gated-at.bofh.it> <pN0ie-3Os-21@gated-at.bofh.it> <pNahz-1uy-13@gated-at.bofh.it> <pNm94-1IO-9@gated-at.bofh.it> <pOjsw-2E2-23@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Mon, Jul 20, 2015 at 02:39:06PM +0100, Will Deacon wrote:
> On Fri, Jul 17, 2015 at 11:14:14PM +0100, Benjamin Herrenschmidt wrote:
> > On Fri, 2015-07-17 at 10:32 +0100, Will Deacon wrote:
> > > static inline void arch_spin_unlock(arch_spinlock_t *lock)
> > > {
> > > - SYNC_IO;
> > > - __asm__ __volatile__("# arch_spin_unlock\n\t"
> > > - PPC_RELEASE_BARRIER: : :"memory");
> > > + smp_mb();
> > > lock->slock = 0;
> > > }
> >
> > That probably needs to be mb() in case somebody has the expectation that
> > it does a barrier vs. DMA on UP.
>
> Hmm, but on !SMP doesn't arch_spin_unlock effectively expand to barrier()
> in the core code?
Yes, to barrier(), but that doesn't generate any code. In contrast, the
mb() that Ben is asking for puts out a sync instruction. Without that
sync instruction, MMIO accesses can be reordered with the spin_unlock(),
even on single-CPU systems. So the bm() is really needed if unlock is
to order against MMIO (and thus DMA) on UP.
Thanx, Paul
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[RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-13 14:20 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Peter Zijlstra <peterz@infradead.org> - 2015-07-14 10:40 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-14 12:10 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-14 21:40 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-15 03:40 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-15 13:00 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-15 15:20 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Michael Ellerman <mpe@ellerman.id.au> - 2015-07-15 05:10 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-15 12:50 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Michael Ellerman <mpe@ellerman.id.au> - 2015-07-16 04:10 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-16 17:20 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2015-07-17 01:00 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-17 11:40 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Peter Zijlstra <peterz@infradead.org> - 2015-07-17 12:20 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-17 14:50 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2015-07-18 00:20 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-20 15:40 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-20 15:50 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon <will.deacon@arm.com> - 2015-07-20 16:00 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-15 16:20 +0200
Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Michael Ellerman <mpe@ellerman.id.au> - 2015-07-16 03:40 +0200
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