Messages in this thread | | | Date | Wed, 3 Aug 2011 21:43:45 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] shm: optimize exit_shm() |
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On 08/03, Vasiliy Kulikov wrote: > > On Wed, Aug 03, 2011 at 21:29 +0200, Oleg Nesterov wrote: > > On 08/03, Vasiliy Kulikov wrote: > > > > > > On Wed, Aug 03, 2011 at 21:08 +0200, Manuel Lauss wrote: > > > > > + > > > > > /* Destroy all already created segments, but not mapped yet */ > > > > > down_write(&shm_ids(ns).rw_mutex); > > > > > if (shm_ids(ns).in_use) > > > > > > > > This check here is now unnecessary, yes? > > > > > > No, as I said in the comment above, other task may be holding the mutex and > > > deleting the last shm segment. So, current task will see in_use == 1 > > > before down_write(), but == 0 after it. > > > > And? Why we can not do idr_for_each() in this (unikely) case? > > Because it's pointless. idr_for_each() would not find any used segment.
This is clear. But it seems that me + Manuel were equally confused by the changelog.
> > > > And this also fixes the oops. > > > > > > Yes, but it only hides the real problem - tasks' dependency on initialized > > > init_*_ns. > > > > This is true, but your patch has the same dependency, but pretends > > it doesn't ;) and it complicates the code. > > I didn't say that .in_use check fixes the oops.
I meant your shm-fix-a-race-between-shm_exit-and-shm_init.patch which should be dropped imho ;)
Oleg.
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