lkml.org 
[lkml]   [2007]   [Oct]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] synchronize_irq needs a barrier
From
Date

> The whole lock/set IRQ_INPROGRESS/unlock path can then only happen
> before the locked section above, in which case we see and wait nicely
> and all is good, or after, in which case the store to foo will be
> visible to the IRQ handler as it will be ordered with the unlock in the
> code above.

Note that napi_synchronize needs a slightly different treatement.

Here, the situation boils down to:

one CPU does:

foo = 1;
while(test_bit(bar))
barrier();
and the other:

if (!test_and_set_bit(bar)) {
read & use foo
smp_mb__before_clear_bit();
clear_bit(bar);
}
The good thing here is that read & use foo is part of the critical
section (I hate hand-made locks ...) defined by bar which makes
things somewhat easier than the synchronize_irq() case.

I think a simple smp_mb(); here after foo = 1; is enough, which means
basically just having an smp_mp(); inside napi_synchronize(), before
the test_bit(). Or do I miss something ?

Cheers,
Ben.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-10-19 06:31    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site