lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <20171013055126.GO10593@eguan.usersys.redhat.com> Date: Fri, 13 Oct 2017 13:51:26 +0800 From: Eryu Guan <eguan@...hat.com> To: Jan Kara <jack@...e.cz> Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, lczerner@...hat.com Subject: Re: [v4.14-rc3 bug] scheduling while atomic in generic/451 test on extN On Thu, Oct 12, 2017 at 09:18:15PM +0200, Jan Kara wrote: > On Fri 13-10-17 00:57:07, Eryu Guan wrote: > > On Thu, Oct 12, 2017 at 05:07:40PM +0200, Jan Kara wrote: > > > Hi Eryu! > > > > > > On Thu 05-10-17 14:07:00, Eryu Guan wrote: > > > > I hit "scheduling while atomic" bug by running fstests generic/451 on > > > > extN filesystems in v4.14-rc3 testing, but it didn't reproduce for me on > > > > every host I tried, but I've seen it multiple times on multiple hosts. A > > > > test vm of mine with 4 vcpus and 8G memory reproduced the bug reliably, > > > > while a bare metal host with 8 cpus and 8G mem couldn't. > > > > > > > > This is due to commit 332391a9935d ("fs: Fix page cache inconsistency > > > > when mixing buffered and AIO DIO"), which defers AIO DIO io completion > > > > to a workqueue if the inode has mapped pages and does page cache > > > > invalidation in process context. I think that the problem is that the > > > > pages can be mapped after the dio->inode->i_mapping->nrpages check, so > > > > we're doing page cache invalidation, which could sleep, in interrupt > > > > context, thus "scheduling while atomic" bug happens. > > > > > > > > Defering all AIO DIO completion to workqueue unconditionally (as what > > > > the iomap based path does) fixed the problem for me. But there're > > > > performance concerns to do so in the original discussions. > > > > > > > > https://www.spinics.net/lists/linux-fsdevel/msg112669.html > > > > > > Thanks for report and the detailed analysis. I think your analysis is > > > correct and the nrpages check in dio_bio_end_aio() is racy. My solution to > > > this would be to pass to dio_complete() as an argument whether invalidation > > > is required or not (and set it to true for deferred completion and to false > > > when we decide not to defer completion since nrpages is 0 at that moment). > > > Lukas? > > > > But wouldn't that bring the original bug back? i.e. read the stale data > > from pagecache, because it's possible that we need to invalidate the > > caches but we didn't. > > I don't think so. dio_bio_end_aio() gets called when the storage has > acknowledged the data is stored. Thus once that is invoked, if we establish > new page cache page, it will be loaded with new data and thus we won't > carry stale data in it. I think you're right, I missed that. Thanks for the explanation! Eryu > > Honza > -- > Jan Kara <jack@...e.com> > SUSE Labs, CR
Powered by blists - more mailing lists