linux-kernel - Re: __sb_start_write() && force

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Date:	Wed, 19 Aug 2015 13:25:26 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: __sb_start_write() && force_trylock hack

On Tue, Aug 18, 2015 at 05:18:16PM +0200, Oleg Nesterov wrote:
> On 08/18, Oleg Nesterov wrote:
> >
> > When I tried to run all tests, I
> > got the new reports from lockdep.
> 
> Just in case... when I run all tests I see misc failures (with or without
> the changes above) which I didn't try to interpret. In particular xfs/073
> just hangs, "shutdown -r" doesn't work, the serial console continues to
> print
> 
> 	[10784.605139] XFS (loop2): metadata I/O error: block 0x7d4948 ("xfs_buf_iodone_callbacks") error 5 numblks 8

EIO from the loop device.

> 	[10784.605207] loop: Write error at byte offset 26843578368, length 4096.
> 	[10784.605222] loop: Write error at byte offset 26843578368, length 4096.
> 	[10784.605235] loop: Write error at byte offset 26843578368, length 4096.
> 	[10784.605248] loop: Write error at byte offset 26843578368, length 4096.
> 	[10784.605261] loop: Write error at byte offset 26843578368, length 4096.

That makes me think the underlying filesystem (i.e. the fs the loop
image file is hosted on) ran out of space. Everything will go to
shit if that happens.

> again and again.
> 
> Plus some tests need a lot of time (for example generic/127 more than 70 minutes!),

Yup, that one only does about 50,000 synchronous writes via fsx.

If you want to run fast, use a virtual machine with 10GB RAM and use
a pair of 4GB ramdisks as the storage.

Or expunge the long running tests (look up the -X option) so they
are skipped.

> Also, tests/generic/078 on 4.2.0-rc6 (without other changes) triggered
> 
> 	[ 2100.404545] BUG: looking up invalid subclass: 8
> 	[ 2100.409600] turning off the locking correctness validator.

That's another lockdep annotation limitation I've had to work
around. The RENAME_WHITEOUT changes caused that by introducing the
need to lock 5 inodes at the same time (src/dst dir, src/dst file,
whiteout inode) instead of only 4.

> perhaps this was fixed by Dave's ILOCK patches.

It greatly complicated those patches, you mean?

But, yes, those patches should have fixed it - I had to shoehorn
about 15 different XFS inode locking subclasses into the 8
subclasses that lockdep supports. And I used all 8 subclasses for
the ILOCK annotations, so if theres some other annotation we need to
add (e.g more than one level of ILOCK_PARENT lock nesting) then,
well, we will need at least 16 subclasses to annotate everything.

I hate lockdep.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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