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@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>