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SubjectRe: [RFC][PATCH 2/4] interruptible rwsem operations (i386, core)
David Howells wrote:
> Dominik Brodowski <linux@dominikbrodowski.de> wrote:
>
>
>>Add functions down_read_interruptible, and down_write_interruptible to rw
>>semaphores. Implement these for i386.
>>...
>
>
>>+static inline int
>>+rwsem_down_interruptible_failed_common(struct rw_semaphore *sem,
>>+ struct rwsem_waiter *waiter, signed long adjustment)
>>+{
>>...
>
>
> I wonder if you should check to see if there are any readers that can be woken
> up if a sleeping writer is interrupted, but I can't think of a simple way to
> do it.
>
>

I think it will, won't it?

>>-struct rw_semaphore fastcall __sched *
>>-rwsem_down_read_failed(struct rw_semaphore *sem)
>>+void fastcall __sched rwsem_down_read_failed(struct rw_semaphore *sem)
>
>
> Please don't.
>
>
>>@@ -199,14 +253,33 @@ rwsem_down_read_failed(struct rw_semapho
>> RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS);
>>
>> rwsemtrace(sem, "Leaving rwsem_down_read_failed");
>>- return sem;
>
>
> Ditto.
>
>
>>-struct rw_semaphore fastcall __sched *
>>-rwsem_down_write_failed(struct rw_semaphore *sem)
>>+void fastcall __sched rwsem_down_write_failed(struct rw_semaphore *sem)
>
>
> Ditto.
>
>
>>@@ -216,10 +289,31 @@ rwsem_down_write_failed(struct rw_semaph
>> rwsem_down_failed_common(sem, &waiter, -RWSEM_ACTIVE_BIAS);
>>
>> rwsemtrace(sem, "Leaving rwsem_down_write_failed");
>>- return sem;
>
>
> Ditto.
>
>
>>@@ -99,11 +103,12 @@ static inline void __down_read(struct rw
>> {
>> __asm__ __volatile__(
>> "# beginning down_read\n\t"
>>-LOCK_PREFIX " incl (%%eax)\n\t" /* adds 0x00000001, returns the old value */
>>+LOCK_PREFIX " incl %0\n\t" /* adds 0x00000001, returns the old value */
>
>
> Ditto.
>
>
>> " js 2f\n\t" /* jump if we weren't granted the lock */
>> "1:\n\t"
>> LOCK_SECTION_START("")
>> "2:\n\t"
>>+ " movl %2,%%eax\n\t"
>
>
> Splat.
>
>
>> " pushl %%ecx\n\t"
>> " pushl %%edx\n\t"
>> " call rwsem_down_read_failed\n\t"
>
>
> Splat.
>
>
>>@@ -113,11 +118,41 @@ LOCK_PREFIX " incl (%%eax)\n\t" /*
>> LOCK_SECTION_END
>> "# ending down_read\n\t"
>> : "=m"(sem->count)
>>- : "a"(sem), "m"(sem->count)
>>+ : "m"(sem->count), "m"(sem)
>> : "memory", "cc");
>> }
>
>
> You appear to be corrupting EAX.
>
>
>>+static inline int __down_read_interruptible(struct rw_semaphore *sem)
>
>
> Will corrupt EAX.
>

I'll fix these up. You're right by the looks.

>
>> "# beginning down_write\n\t"
>>-LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtract 0x0000ffff, returns the old value */
>>+LOCK_PREFIX " xadd %%edx,%0\n\t" /* subtract 0x0000ffff, returns the old value */
>
>
> Again, please don't. It's a lot more readable when it mentions EAX directly,
> plus it's also independent of constraint reordering.
>

OK I suppose so...


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