On Mar 17, 2013, at 6:49 PM, NeilBrown wrote:

On Wed, 13 Mar 2013 12:29:24 -0500 Jonathan Brassow [off-list ref]
wrote:

quoted

Neil,

I've noticed that when too many devices fail in a RAID arrary that
addtional I/O will hang, yielding an endless supply of:
Mar 12 11:52:53 bp-01 kernel: Buffer I/O error on device md1, logical block 3
Mar 12 11:52:53 bp-01 kernel: lost page write due to I/O error on md1
Mar 12 11:52:53 bp-01 kernel: sector=800 i=3           (null)           (null)  
        (null)           (null) 1

This is the third report in as many weeks that mentions that WARN_ON.
The first two where quite different causes.
I think this one is the same as the first one, which means it would be fixed
by  
     md/raid5: schedule_construction should abort if nothing to do.

which is commit 29d90fa2adbdd9f in linux-next.

Sorry, I don't see this commit in linux-next:
(the "for-next" branch of) git://github.com/neilbrown/linux.git
or git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git

Where should I be looking?

I did grab a patch from an earlier discussion where you mentioned a similar commit ID.  It didn't solve the problem, but it did prevent an endless progression of the same error messages.  I only saw one instance of the above after the patch.

I'm fairly certain that the hang was affecting more than just RAID5 though.  It also happened with raid1/10.  I'll go back with 3.9.0-rc3 and make sure that's true until I can figure out which 'linux-next' commit you are talking about.

thanks,
 brassow