On Wed, 18 Apr 2007, Derrick J Brashear wrote:
On Wed, 18 Apr 2007, Chaskiel M Grundman wrote:
--On Wednesday, April 18, 2007 02:45:36 PM -0400 Christopher Allen Wing
<[EMAIL PROTECTED]> wrote:
I don't understand the usage of AFS_GLOCK(); why is it safe to drop and
re-acquire it in cases like this? Is AFS_GLOCK intended to serialize all
AFS calls coming from vnode methods in the kernel?
AFS_GLOCK is intended to prevent smp concurrency (and preemption). It also
provides mutual exclusion for ObtainXXXLock. AFS_GLOCK is dropped almost
any time the cache manager is going to sleep.
Of course that doesn't make it necessarily safe to drop and reacquire. In
practice we've just attempted to make it safe every time it's cropped up that
it's not.
The __vmalloc approach would be safer if we were even vaguely sure that it
was exported in enough cases.
__vmalloc() is exported from linux-2.4.0 up to and including today's
source tree. GFP_NOFS didn't exist until midway through 2.4 anyway, so
it's a moot point if we have to use vmalloc() instead for <= 2.4.
(actually, in 2.4 kernels vmalloc() is an inline function in a header file
and only __vmalloc() is exported; in 2.6, both are symbols)
The way that vmalloc() calls __vmalloc() hasn't ever changed, so it should
be a relatively safe change. (might need to include another kernel header
though to get the correct defines and typedefs)
-Chris Wing
[EMAIL PROTECTED]
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