lkml.org 
[lkml]   [2022]   [Aug]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 10/14] locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read_locked()
On Mon, Jul 04, 2022 at 05:05:10PM +0200, Marco Elver wrote:

> +bool percpu_is_read_locked(struct percpu_rw_semaphore *sem)
> +{
> + return per_cpu_sum(*sem->read_count) != 0;
> +}
> +EXPORT_SYMBOL_GPL(percpu_is_read_locked);

I don't think this is correct; read_count can have spurious increments.

If we look at __percpu_down_read_trylock(), it does roughly something
like this:

this_cpu_inc(*sem->read_count);
smp_mb();
if (!sem->block)
return true;
this_cpu_dec(*sem->read_count);
return false;

So percpu_is_read_locked() needs to ensure the read_count is non-zero
*and* that block is not set.

That said; I really dislike the whole _is_locked family with a passion.
Let me try and figure out what you need this for.

\
 
 \ /
  Last update: 2022-08-17 14:50    [W:0.272 / U:0.296 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site