[Skiboot] [PATCH] core/lock: Stop drop_my_locks() from always causing abort

[Vasant Hegde]

On 01/19/2019 01:31 AM, Reza Arbab wrote:
> The loop in drop_my_locks() looks like this:
> 
> 	while((l = list_pop(&this_cpu()->locks_held, struct lock, list)) != NULL) {
> 		if (warn)
> 			prlog(PR_ERR, "  %s\n", l->owner);
> 		unlock(l);
> 	}
> 
> Both list_pop() and unlock() call list_del(). This means that on the
> last iteration of the loop, the list will be empty when we get to
> unlock_check(), causing this:
> 
>    LOCK ERROR: Releasing lock we don't hold depth @0x30493d20 (state: 0x0000000000000001)
>    [13836.000173140,0] Aborting!
>    CPU 0000 Backtrace:
>     S: 0000000031c03930 R: 000000003001d840   ._abort+0x60
>     S: 0000000031c039c0 R: 000000003001a0c4   .lock_error+0x64
>     S: 0000000031c03a50 R: 0000000030019c70   .unlock+0x54
>     S: 0000000031c03af0 R: 000000003001a040   .drop_my_locks+0xf4
> 
> To fix this, change list_pop() to list_top().
> 
> Signed-off-by: Reza Arbab <arbab at linux.ibm.com>

Reviewed-by: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>


@Stewart,
   I think we should pick this for Stable branch. #6.0+

-Vasant