Re: [PATCH v2 06/28] locking/rwlocks: Add contention detection for rwlocks

[Guenter Roeck]

On Tue, Feb 02, 2021 at 10:57:12AM -0800, Ben Gardon wrote:
> rwlocks do not currently have any facility to detect contention
> like spinlocks do. In order to allow users of rwlocks to better manage
> latency, add contention detection for queued rwlocks.
> 
> CC: Ingo Molnar <mingo@xxxxxxxxxx>
> CC: Will Deacon <will@xxxxxxxxxx>
> Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>
> Acked-by: Waiman Long <longman@xxxxxxxxxx>
> Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>

When building mips:defconfig, this patch results in:

Error log:
In file included from include/linux/spinlock.h:90,
                 from include/linux/ipc.h:5,
                 from include/uapi/linux/sem.h:5,
                 from include/linux/sem.h:5,
                 from include/linux/compat.h:14,
                 from arch/mips/kernel/asm-offsets.c:12:
arch/mips/include/asm/spinlock.h:17:28: error: redefinition of 'queued_spin_unlock'
   17 | #define queued_spin_unlock queued_spin_unlock
      |                            ^~~~~~~~~~~~~~~~~~
arch/mips/include/asm/spinlock.h:22:20: note: in expansion of macro 'queued_spin_unlock'
   22 | static inline void queued_spin_unlock(struct qspinlock *lock)
      |                    ^~~~~~~~~~~~~~~~~~
In file included from include/asm-generic/qrwlock.h:17,
                 from ./arch/mips/include/generated/asm/qrwlock.h:1,
                 from arch/mips/include/asm/spinlock.h:13,
                 from include/linux/spinlock.h:90,
                 from include/linux/ipc.h:5,
                 from include/uapi/linux/sem.h:5,
                 from include/linux/sem.h:5,
                 from include/linux/compat.h:14,
                 from arch/mips/kernel/asm-offsets.c:12:
include/asm-generic/qspinlock.h:94:29: note: previous definition of 'queued_spin_unlock' was here
   94 | static __always_inline void queued_spin_unlock(struct qspinlock *lock)
      |                             ^~~~~~~~~~~~~~~~~~

Bisect log attached.

Guenter

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# bad: [a4bfd8d46ac357c12529e4eebb6c89502b03ecc9] Add linux-next specific files for 20210209
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# bad: [f3d4b4b1dc1c5fb9ea17cac14133463bfe72f170] sched: Add cond_resched_rwlock
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# good: [f1b3b06a058bb5c636ffad0afae138fe30775881] KVM: x86/mmu: Clear dirtied pages mask bit before early break
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# bad: [26128cb6c7e6731fe644c687af97733adfdb5ee9] locking/rwlocks: Add contention detection for rwlocks
git bisect bad 26128cb6c7e6731fe644c687af97733adfdb5ee9
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# first bad commit: [26128cb6c7e6731fe644c687af97733adfdb5ee9] locking/rwlocks: Add contention detection for rwlocks