svn commit: r296947 - head/share/man/man9

[Bryan Drewery]

On 3/16/2016 11:45 AM, Konstantin Belousov wrote:
> On Wed, Mar 16, 2016 at 06:39:48PM +0000, Bryan Drewery wrote:
>> Author: bdrewery
>> Date: Wed Mar 16 18:39:48 2016
>> New Revision: 296947
>> URL: https://svnweb.freebsd.org/changeset/base/296947
>>
>> Log:
>>   Remove incorrect BUGS entry about asserting lock not held.
>>   
>>   For non-WITNESS< assertion support for SA_UNLOCKED was added in r125421 and
>>   made to panic in r126316.
>>   
>>   MFC after:	1 week
>>
>> Modified:
>>   head/share/man/man9/sx.9
>>
>> Modified: head/share/man/man9/sx.9
>> ==============================================================================
>> --- head/share/man/man9/sx.9	Wed Mar 16 17:35:55 2016	(r296946)
>> +++ head/share/man/man9/sx.9	Wed Mar 16 18:39:48 2016	(r296947)
>> @@ -26,7 +26,7 @@
>>  .\"
>>  .\" $FreeBSD$
>>  .\"
>> -.Dd March 13, 2016
>> +.Dd March 16, 2016
>>  .Dt SX 9
>>  .Os
>>  .Sh NAME
>> @@ -320,11 +320,6 @@ end up sleeping while holding a mutex, w
>>  .Xr rwlock 9 ,
>>  .Xr sema 9
>>  .Sh BUGS
>> -Currently there is no way to assert that a lock is not held.
>> -This is not possible in the
>> -.No non- Ns Dv WITNESS
>> -case for asserting that this thread
>> -does not hold a shared lock.
>>  In the
>>  .No non- Ns Dv WITNESS
>>  case, the
> The removed text was not quite correct, but its removal is not quite correct
> either.  sx (and rw) locks do not track shared owners, so in non-witness
> case only exclusive ownership by curthread triggers panic for SA_UNLOCKED
> case.  Shared ownership is silently ignored by the assert.
> 

Yes you're right. The original change for this in r125421 was checking
shared count:

> Index: head/sys/kern/kern_sx.c
> ===================================================================
> --- head/sys/kern/kern_sx.c     (revision 125420)
> +++ head/sys/kern/kern_sx.c     (revision 125421)
> @@ -344,6 +344,17 @@
>                             sx->sx_object.lo_name, file, line);
>                 mtx_unlock(sx->sx_lock);
>                 break;
> +       case SX_UNLOCKED:
> +#ifdef WITNESS
> +               witness_assert(&sx->sx_object, what, file, line);
> +#else
> +               mtx_lock(sx->sx_lock);
> +               if (sx->sx_cnt != 0 && sx->sx_xholder == curthread)
> +                       printf("Lock %s locked @ %s:%d\n",
> +                           sx->sx_object.lo_name, file, line);
> +               mtx_unlock(sx->sx_lock);
> +#endif
> +               break;
>         default:
>                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
>                     line);

But it was later removed in r126003:

> Index: head/sys/kern/kern_sx.c
> ===================================================================
> --- head/sys/kern/kern_sx.c     (revision 126002)
> +++ head/sys/kern/kern_sx.c     (revision 126003)
> @@ -348,8 +348,12 @@
>  #ifdef WITNESS
>                 witness_assert(&sx->sx_object, what, file, line);
>  #else
> +               /*
> +                * We are able to check only exclusive lock here,
> +                * we cannot assert that *this* thread owns slock.
> +                */
>                 mtx_lock(sx->sx_lock);
> -               if (sx->sx_cnt != 0 && sx->sx_xholder == curthread)
> +               if (sx->sx_xholder == curthread)
>                         printf("Lock %s locked @ %s:%d\n",
>                             sx->sx_object.lo_name, file, line);
>                 mtx_unlock(sx->sx_lock);


I incorrectly was looking at only the original code and the panic fix,
rather than current code to ensure it still was checking shared lock
holders.

-- 
Regards,
Bryan Drewery

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