From: Steven Rostedt <rostedt@goodmis.org>
To: Christoph Hellwig <hch@lst.de>
Cc: akpm@linux-foundation.org, joelaf@google.com,
jszhang@marvell.com, chris@chris-wilson.co.uk,
joaodias@google.com, linux-mm@kvack.org,
linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/6] mm: add preempt points into __purge_vmap_area_lazy
Date: Tue, 18 Oct 2016 17:01:47 -0400 [thread overview]
Message-ID: <20161018170147.232aed1e@gandalf.local.home> (raw)
In-Reply-To: <20161018205648.GB7021@home.goodmis.org>
On Tue, 18 Oct 2016 16:56:48 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> Is releasing the lock within a llist_for_each_entry_safe() actually safe? Is
> vmap_area_lock the one to protect the valist?
>
> That is llist_for_each_entry_safe(va, n_va, valist, purg_list) does:
>
> for (va = llist_entry(valist, typeof(*va), purge_list);
> &va->purge_list != NULL &&
> n_va = llist_entry(va->purge_list.next, typeof(*n_va),
> purge_list, true);
> pos = n)
>
> Thus n_va is pointing to the next element to process when we release the
> lock. Is it possible for another task to get into this same path and process
> the item that n_va is pointing to? Then when the preempted task comes back,
> grabs the vmap_area_lock, and then continues the loop with what n_va has,
> could that cause problems? That is, the next iteration after releasing the
> lock does va = n_va. What happens if n_va no longer exits?
>
> I don't know this code that well, and perhaps vmap_area_lock is not protecting
> the list and this is all fine.
>
Bah, nevermind. I missed the:
valist = llist_del_all(&vmap_purge_list);
so yeah, all should be good.
Nothing to see here, move along please.
-- Steve
next prev parent reply other threads:[~2016-10-18 21:01 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-18 6:56 [RFC] reduce latency in __purge_vmap_area_lazy Christoph Hellwig
2016-10-18 6:56 ` [PATCH 1/6] mm: refactor __purge_vmap_area_lazy Christoph Hellwig
2016-10-18 6:56 ` [PATCH 2/6] mm: mark all calls into the vmalloc subsystem as potentially sleeping Christoph Hellwig
2016-10-18 10:33 ` Chris Wilson
2016-10-18 10:38 ` Christoph Hellwig
2016-10-19 11:15 ` Chris Wilson
2016-10-19 13:05 ` Christoph Hellwig
2016-10-19 15:34 ` Andy Lutomirski
2016-10-19 16:31 ` Christoph Hellwig
2016-10-19 19:43 ` Chris Wilson
2016-10-21 0:32 ` Joel Fernandes
2016-11-08 13:24 ` Joel Fernandes
2016-11-08 14:32 ` Andrey Ryabinin
2016-10-18 6:56 ` [PATCH 3/6] mm: remove free_unmap_vmap_area_noflush Christoph Hellwig
2016-10-18 6:56 ` [PATCH 4/6] mm: remove free_unmap_vmap_area_addr Christoph Hellwig
2016-10-21 0:46 ` Joel Fernandes
2016-10-21 1:58 ` Nicholas Piggin
2016-10-18 6:56 ` [PATCH 5/6] mm: turn vmap_purge_lock into a mutex Christoph Hellwig
2016-10-18 6:56 ` [PATCH 6/6] mm: add preempt points into __purge_vmap_area_lazy Christoph Hellwig
2016-10-18 20:56 ` Steven Rostedt
2016-10-18 21:01 ` Steven Rostedt [this message]
2016-10-18 10:40 ` [RFC] reduce latency in __purge_vmap_area_lazy Nicholas Piggin
2016-10-18 11:21 ` Jisheng Zhang
2016-10-21 1:08 ` Joel Fernandes
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