[BUG] reproducable ubifs reboot assert and corruption

[richard@nod.at (Richard Weinberger)]

Am 29.01.2014 06:32, schrieb Andrew Ruder:
> Ok, I've got some more useful information.  I have been adding
> a multitude of WARN_ON's and prink's all over the remount code and have
> come up with the attached log.
> 
> A little bit of explanation:
> 
> Line 1: sync_filesystem (from do_remount_sb)
> Line 188: sync_filesystem ends
> Line 43, 64, 81, 98, 114, 135, 156, 173: write operations that occur
> during sync_filesystem.  Before each warning I print the inode pointer.
> Line 197: read-only remount has completely finished (this message is
> from userspace post remount)
> Line 199: a sync is called, there are apparently dirty inodes in our
> now-readonly ubifs filesystem
> Line 215: failed assert that occurs because the writeback triggers for
> inode 0xd75b9450 (see line 41, it got in with a sys_write while we were
> running our sync_filesystem in do_remount_sb)
> 
> Does this help?  It looks like there is a race condition between the
> writeback code and the remount read-only.  Nothing is done to lock out
> writes during the first half of the do_remount_sb and some stuff makes
> it into the writeback worker queue while we are busy syncing the
> filesystem only to trigger later when ubifs has decided it is
> read-only...

So you can trigger this by running fsstress on /mnt and then call
mount -o remount,ro /mnt?

Can you also trigger it on nandsim or mtdram?

I did a quick test on my testbed using mtdram and was unable to trigger it.
But I fear my box is too fast.

Thanks,
//richard