* [PATCH] Lockdep treats down_write_trylock like regular down_write
@ 2007-04-09 9:56 Pavel Emelianov
2007-04-09 15:09 ` Arjan van de Ven
0 siblings, 1 reply; 3+ messages in thread
From: Pavel Emelianov @ 2007-04-09 9:56 UTC (permalink / raw)
To: Andrew Morton; +Cc: Ingo Molnar, Arjan van de Ven, Linux Kernel Mailing List
[-- Attachment #1: Type: text/plain, Size: 282 bytes --]
This causes constructions like
down_write(&mm1->mmap_sem);
if (down_write_trylock(&mm2->mmap_sem)) {
...
up_write(&mm2->mmap_sem);
}
up_write(&mm1->mmap_sem);
generate a lockdep warning about circular locking dependence.
Call rwsem_acquire() with trylock set to 1.
[-- Attachment #2: diff-lockdep-rwsem-trylock --]
[-- Type: text/plain, Size: 356 bytes --]
--- ./kernel/rwsem.c.pbonrem 2007-03-06 19:09:50.000000000 +0300
+++ ./kernel/rwsem.c 2007-04-06 14:02:18.000000000 +0400
@@ -60,7 +60,7 @@ int down_write_trylock(struct rw_semapho
int ret = __down_write_trylock(sem);
if (ret == 1)
- rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
+ rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
return ret;
}
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Lockdep treats down_write_trylock like regular down_write
2007-04-09 9:56 [PATCH] Lockdep treats down_write_trylock like regular down_write Pavel Emelianov
@ 2007-04-09 15:09 ` Arjan van de Ven
2007-04-10 7:37 ` Pavel Emelianov
0 siblings, 1 reply; 3+ messages in thread
From: Arjan van de Ven @ 2007-04-09 15:09 UTC (permalink / raw)
To: Pavel Emelianov; +Cc: Andrew Morton, Ingo Molnar, Linux Kernel Mailing List
Pavel Emelianov wrote:
> This causes constructions like
>
> down_write(&mm1->mmap_sem);
> if (down_write_trylock(&mm2->mmap_sem)) {
> ...
> up_write(&mm2->mmap_sem);
> }
> up_write(&mm1->mmap_sem);
>
> generate a lockdep warning about circular locking dependence.
please show me why this is safe, especially if you intermix it with
down_read()'s... like copy_to_user and co may do.
this feels like a very unsafe construct to me...
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Lockdep treats down_write_trylock like regular down_write
2007-04-09 15:09 ` Arjan van de Ven
@ 2007-04-10 7:37 ` Pavel Emelianov
0 siblings, 0 replies; 3+ messages in thread
From: Pavel Emelianov @ 2007-04-10 7:37 UTC (permalink / raw)
To: Arjan van de Ven; +Cc: Andrew Morton, Ingo Molnar, Linux Kernel Mailing List
Arjan van de Ven wrote:
> Pavel Emelianov wrote:
>> This causes constructions like
>>
>> down_write(&mm1->mmap_sem);
>> if (down_write_trylock(&mm2->mmap_sem)) {
>> ...
>> up_write(&mm2->mmap_sem);
>> }
>> up_write(&mm1->mmap_sem);
>>
>> generate a lockdep warning about circular locking dependence.
>
> please show me why this is safe, especially if you intermix it with
> down_read()'s... like copy_to_user and co may do.
This is safe as once the task locks the mm1->mmap_sem and gets
into '...' place it is *running* and will release booth semaphores
for sure.
> this feels like a very unsafe construct to me...
>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2007-04-10 7:35 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2007-04-09 9:56 [PATCH] Lockdep treats down_write_trylock like regular down_write Pavel Emelianov
2007-04-09 15:09 ` Arjan van de Ven
2007-04-10 7:37 ` Pavel Emelianov
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox