lkml.org 
[lkml]   [2008]   [Aug]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [ANNOUNCE] mdb-2.6.27-rc2-ia32-08-07-08.patch
Stefan Richter wrote:
> jmerkey@wolfmountaingroup.com wrote:
>
>> The mdb-rc2 patch was posted this morning with the changes for a modular
>> kernel debugger using kprobes.
>>
>> ftp://ftp.wolfmountaingroup.org/pub/mdb/mdb-2.6.27-rc2-ia32-08-07-08.patch
>>
>> Jeffrey Vernon Merkey
>>
>
>
> Quoting from this patch:
>
>
>> +typedef struct _RLOCK
>> +{
>> +#if defined(CONFIG_SMP)
>> + spinlock_t lock;
>> +#endif
>> + unsigned long flags;
>> + unsigned long processor;
>> + unsigned long count;
>> +} rlock_t;
>>
>
> Is this something along the lines of a counting semaphore? As far as I
> understand its accessor functions, an rlock
> - can be taken by one CPU multiple times,
> - will block the other CPUs as long as the first CPU hasn't unlocked
> the rlock as many times as it locked it.
>
> The accessors rspin_lock() and rspin_try_lock() peek into spinlock_t and
> may therefore not be fully portable. Also, they and rspin_unlock()
> don't look SMP safe:
>
>
>> +//
>> +// returns 0 - atomic lock occurred, processor assigned
>> +// 1 - recusive count increased
>> +//
>> +
>> +unsigned long rspin_lock(volatile rlock_t *rlock)
>> +{
>> +#if defined(CONFIG_SMP)
>> + register unsigned long proc = get_processor_id();
>> + register unsigned long retCode;
>> +
>> + if (rlock->lock.raw_lock.slock && rlock->processor == proc)
>>

Ticket locks will almost always have a non-zero slock. It doesn't
indicate anything about the locked/unlocked state. But this looks like
it's effectively doing a trylock:

if (!spin_trylock(rlock) && rlock->processor == proc) {
rlock->count++;
...
} else {
rlock->processor = proc;
...
}


J




\
 
 \ /
  Last update: 2008-08-09 07:09    [W:0.079 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site