linux-ext4 - Re: [PATCH 3/3] ext4: Gracefully handle ext4_break

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Date:   Fri, 24 May 2019 23:32:35 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH 3/3] ext4: Gracefully handle ext4_break_layouts() failure
 during truncate

On Wed, May 22, 2019 at 11:03:17AM +0200, Jan Kara wrote:
> ext4_break_layouts() may fail e.g. due to a signal being delivered.
> Thus we need to handle its failure gracefully and not by taking the
> filesystem down. Currently ext4_break_layouts() failure is rare but it
> may become more common once RDMA uses layout leases for handling
> long-term page pins for DAX mappings.
> 
> To handle the failure we need to move ext4_break_layouts() earlier
> during setattr handling before we do hard to undo changes such as
> modifying inode size. To be able to do that we also have to move some
> other checks which are better done without holding i_mmap_sem earlier.
> 
> Reported-and-tested-by: Ira Weiny <ira.weiny@...el.com>
> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Jan Kara <jack@...e.cz>

When doing some final testing before sending a pull request to Linus,
I found a regression.  After bisecting, this patch fails reliably
under gce-xfstests:

TESTRUNID: tytso-20190524230226
KERNEL:    kernel 5.1.0-rc3-xfstests-00039-g079f9927c7bf #1016 SMP Fri May 24 23:00:47 EDT 2019 x86_64
CMDLINE:   -c 4k generic/092
CPUS:      2
MEM:       7680

ext4/4k: 1 tests, 1 failures, 2 seconds
  generic/092  Failed   1s
Totals: 1 tests, 0 skipped, 1 failures, 0 errors, 1s

FSTESTPRJ: gce-xfstests
FSTESTVER: fio  fio-3.2 (Fri, 3 Nov 2017 15:23:49 -0600)
FSTESTVER: quota  62661bd (Tue, 2 Apr 2019 17:04:37 +0200)
FSTESTVER: xfsprogs v5.0.0 (Fri, 3 May 2019 12:14:36 -0500)
FSTESTVER: xfstests-bld 9582562 (Sun, 12 May 2019 00:38:51 -0400)
FSTESTVER: xfstests linux-v3.8-2390-g64233614 (Thu, 16 May 2019 00:12:52 -0400)
FSTESTCFG: 4k
FSTESTSET: generic/092
FSTESTOPT: aex
GCE ID:    343197219467628221

generic/092 0s ... 	[23:05:07] [23:05:08]- output mismatch (see /results/ext4/results-4k/generic/092
.out.bad)
% diff -u /tmp/results-tytso-20190524230226/ext4/results-4k/generic/092.out.bad /usr/projects/xfstests-bld/build-64/xfstests-dev/tests/generic/092.out 
--- /tmp/results-tytso-20190524230226/ext4/results-4k/generic/092.out.bad	2019-05-24 23:05:08.000000000 -0400
+++ /usr/projects/xfstests-bld/build-64/xfstests-dev/tests/generic/092.out	2018-02-13 23:37:20.330097382 -0500
@@ -2,6 +2,5 @@
 wrote 5242880/5242880 bytes at offset 0
 XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 0: [0..10239]: data
-1: [10240..20479]: unwritten
 0: [0..10239]: data
 1: [10240..20479]: unwritten


Dropping this patch makes the test failure go away.  So I'm going to
drop it for now.  Jan, can you take a look?  Thanks!!

	      	    	      	   	      - Ted