Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sun, 8 May 2011 16:51:28 +0400 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH v2] tmpfs: fix race between umount and writepage |
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Hugh Dickins wrote: > On Sat, 7 May 2011, Konstantin Khlebnikov wrote: >> Hugh Dickins wrote: >> >>> Here's the patch I was testing last night, but I do want to test it >>> some more (I've not even tried your unmounting case yet), and I do want >>> to make some changes to it (some comments, and see if I can move the >>> mem_cgroup_cache_charge outside of the mutex, making it GFP_KERNEL >>> rather than GFP_NOFS - at the time that mem_cgroup charging went in, >>> we did not know here if it was actually a shmem swap page, whereas >>> nowadays we can be sure, since that's noted in the swap_map). >>> >>> In shmem_unuse_inode I'm widening the shmem_swaplist_mutex to protect >>> against shmem_evict_inode; and in shmem_writepage adding to the list >>> earlier, while holding lock on page still in pagecache to protect it. >>> >>> But testing last night showed corruption on this laptop (no problem >>> on other machines): I'm guessing it's unrelated, but I can't be sure >>> of that without more extended testing. >> >> This patch fixed my problem, I didn't catch any crashes on my test-case: >> swapout-unmount. > > Thank you, Konstantin, for testing that and reporting back. > > I tried using your script on Thursday, but couldn't get the tuning right > for this machine: with numbers too big everything would go OOM, with > numbers too small it wouldn't even go to swap, with numbers on the edge > it would soon settle into a steady state with almost nothing in swap. > > Just once, without the patch, I did get to "Self-destruct in 5 seconds", > but that was not reproducible enough for me to test that the patch would > be fixing anything. > > I was going to try today on other machines with more cpus and more memory, > though not as much as yours; but now I'll let your report save me the time, > and just add your Tested-by. Big thank you for that! > > Besides adding comments, I have changed the patch around since then, at > the shmem_unuse_inode end: to avoid any memory allocation while holding > the mutex (and then we no longer need to drop and retake info->lock, > so it gets a little simpler). It would be dishonest of me to claim your > Tested-by for the changed code (and your mount/write/umount loop would > not have been testing swapoff): since it is an independent fix with a > different justification, I'll split that part off into a 2/3.
Ok, I can test final patch-set on the next week. Also I can try to add some swapoff test-cases.
> > 3/3 being the fix to the "corruption" I noticed while testing, corruption > being on the filesystem I had on /dev/loop0, over a tmpfs file filling its > filesystem: when I wrote, I'd missed the "I/O" errors in /var/log/messages. > > It was another case of a long-standing but largely theoretical race, > now made easily reproducible by recent changes (the preallocation in > between find_lock_page and taking info->lock): when the filesystem is > full, you could get ENOSPC from a race in bringing back a previously > allocated page from swap. > > I'll write these three up now and send off to Andrew. > > Hugh
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