Messages in this thread Patch in this message | | | Date | Wed, 30 Jun 2010 12:51:21 -0700 | From | Andrew Morton <> | Subject | Re: [S+Q 01/16] [PATCH] ipc/sem.c: Bugfix for semop() not reporting successful operation |
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On Wed, 30 Jun 2010 21:38:43 +0200 Manfred Spraul <manfred@colorfullife.com> wrote:
> Hi Andrew, > > On 06/29/2010 09:08 PM, Andrew Morton wrote: > > On Tue, 29 Jun 2010 10:42:42 -0500 (CDT) > > Christoph Lameter<cl@linux-foundation.org> wrote: > > > > > >> This is a patch from Manfred. Required to make 2.6.35-rc3 work. > >> > >> > > My current version of the patch is below. > > > > I believe that Luca has still seen problems with this patch applied so > > its current status is "stuck, awaiting developments". > > > > Is that a correct determination? > > > > I would propose that you forward a patch to Linus - either the one you > have in your tree or the v2 that I've just posted.
OK, I added the incremental change:
--- a/ipc/sem.c~ipc-semc-bugfix-for-semop-not-reporting-successful-operation-update +++ a/ipc/sem.c @@ -1440,7 +1440,14 @@ SYSCALL_DEFINE4(semtimedop, int, semid, if (error != -EINTR) { /* fast path: update_queue already obtained all requested - * resources */ + * resources. + * Perform a smp_mb(): User space could assume that semop() + * is a memory barrier: Without the mb(), the cpu could + * speculatively read in user space stale data that was + * overwritten by the previous owner of the semaphore. + */ + smp_mb(); + goto out_free; } _ > With stock 2.6.35-rc3, my semtimedop() stress tests produces an oops or > an invalid return value (i.e.:semtimedop() returns with "1") within a > fraction of a second. > > With either of the patches applied, my test apps show the expected behavior.
OK, I'll queue it up.
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