Messages in this thread | | | Date | Fri, 24 Aug 2012 08:28:45 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH 0/2] revert changes to zcache_do_preload() |
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On Thu, Aug 23, 2012 at 05:10:00PM -0500, Seth Jennings wrote: > On 08/23/2012 03:56 PM, Minchan Kim wrote: > > Hi Seth, > > > > On Thu, Aug 23, 2012 at 10:33:09AM -0500, Seth Jennings wrote: > >> This patchset fixes a regression in 3.6 by reverting two dependent > >> commits that made changes to zcache_do_preload(). > >> > >> The commits undermine an assumption made by tmem_put() in > >> the cleancache path that preemption is disabled. This change > >> introduces a race condition that can result in the wrong page > >> being returned by tmem_get(), causing assorted errors (segfaults, > >> apparent file corruption, etc) in userspace. > >> > >> The corruption was discussed in this thread: > >> https://lkml.org/lkml/2012/8/17/494 > > > > I think changelog isn't enough to explain what's the race. > > Could you write it down in detail? > > I didn't come upon this solution via code inspection, but > rather through discovering that the issue didn't exist in > v3.5 and just looking at the changes since then.
Okay, then, why do you think the patchsets are culprit? I didn't look the cleanup patch series of Xiao at that time so I can be wrong but as I just look through patch of "zcache: optimize zcache_do_preload", I can't find any fault because zcache_put_page checks irq_disable so we don't need to disable preemption so it seems that patch is correct to me. If the race happens by preemption, BUG_ON in zcache_put_page should catch it.
What do you mean? Do you have any clue in your mind?
The commits undermine an assumption made by tmem_put() in the cleancache path that preemption is disabled.
> > > And you should Cc'ed Xiao who is author of reverted patch. > > Thanks for adding Xiao. I meant to do this. For some reason > I thought that you submitted that patchset :-/
Even, I didn't notice that patchset at that time. :)
> My bad. > > Seth > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
-- Kind regards, Minchan Kim
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