[Qemu-devel] [PATCH 0/2] block/file-posix: Fix xfs_write_zeroes()

[Qemu-devel] [PATCH 0/2] block/file-posix: Fix xfs_write_zeroes()

[Max Reitz]

Lukàš ran over a nasty regression in our xfs_write_zeroes() function
(sorry, my fault) made apparent by a recent patch from Anton that makes
qcow2 images heavily exercise the offending code path.

This series fixes the bug and adds a test to prevent it from
reoccurring.


Max Reitz (2):
  block/file-posix: Fix xfs_write_zeroes()
  iotests: Test reverse sub-cluster qcow2 writes

 block/file-posix.c         | 16 ++++++---
 tests/qemu-iotests/265     | 67 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/265.out |  6 ++++
 tests/qemu-iotests/group   |  1 +
 4 files changed, 85 insertions(+), 5 deletions(-)
 create mode 100755 tests/qemu-iotests/265
 create mode 100644 tests/qemu-iotests/265.out

-- 
2.21.0

[Qemu-devel] [PATCH 1/2] block/file-posix: Fix xfs_write_zeroes()

[Max Reitz]

Calling ftruncate() in xfs_write_zeroes() is dangerous because it may
yield and then discard data that parallel write requests have written
past the old EOF in the meantime.  We must not use it here.

Instead, return -ENOTSUP and let the more generic fallocate code handle
writing zeroes past the EOF.

Reported-by: Lukáš Doktor <ldoktor@redhat.com>
Fixes: 50ba5b2d994853b38fed10e0841b119da0f8b8e5
Cc: qemu-stable@nongnu.org
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/file-posix.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index fbeb0068db..b49e0784a4 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -1472,10 +1472,13 @@ static int xfs_write_zeroes(BDRVRawState *s, int64_t offset, uint64_t bytes)
     }
 
     if (offset + bytes > len) {
-        /* XFS_IOC_ZERO_RANGE does not increase the file length */
-        if (ftruncate(s->fd, offset + bytes) < 0) {
-            return -errno;
-        }
+        /*
+         * XFS_IOC_ZERO_RANGE does not increase the file length, but
+         * the caller probably wants us to.
+         * Calling ftruncate() would not be safe, so let the generic
+         * implementation handle this case.
+         */
+        return -ENOTSUP;
     }
 
     memset(&fl, 0, sizeof(fl));
@@ -1580,7 +1583,10 @@ static int handle_aiocb_write_zeroes(void *opaque)
 
 #ifdef CONFIG_XFS
     if (s->is_xfs) {
-        return xfs_write_zeroes(s, aiocb->aio_offset, aiocb->aio_nbytes);
+        int ret = xfs_write_zeroes(s, aiocb->aio_offset, aiocb->aio_nbytes);
+        if (ret != -ENOTSUP) {
+            return ret;
+        }
     }
 #endif
 
-- 
2.21.0

[Qemu-devel] [PATCH 2/2] iotests: Test reverse sub-cluster qcow2 writes

[Max Reitz]

This exercises the regression introduced in commit
50ba5b2d994853b38fed10e0841b119da0f8b8e5.  On my machine, it has close
to a 50 % false-negative rate, but that should still be sufficient to
test the fix.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 tests/qemu-iotests/265     | 67 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/265.out |  6 ++++
 tests/qemu-iotests/group   |  1 +
 3 files changed, 74 insertions(+)
 create mode 100755 tests/qemu-iotests/265
 create mode 100644 tests/qemu-iotests/265.out

diff --git a/tests/qemu-iotests/265 b/tests/qemu-iotests/265
new file mode 100755
index 0000000000..dce6f77be3
--- /dev/null
+++ b/tests/qemu-iotests/265
@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+#
+# Test reverse-ordered qcow2 writes on a sub-cluster level
+#
+# Copyright (C) 2019 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+seq=$(basename $0)
+echo "QA output created by $seq"
+
+status=1	# failure is the default!
+
+_cleanup()
+{
+    _cleanup_test_img
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+
+# qcow2-specific test
+_supported_fmt qcow2
+_supported_proto file
+_supported_os Linux
+
+echo '--- Writing to the image ---'
+
+# Reduce cluster size so we get more and quicker I/O
+IMGOPTS='cluster_size=4096' _make_test_img 1M
+(for ((kb = 1024 - 4; kb >= 0; kb -= 4)); do \
+     echo "aio_write -P 42 $((kb + 1))k 2k"; \
+ done) \
+ | $QEMU_IO "$TEST_IMG" > /dev/null
+
+echo '--- Verifying its content ---'
+
+(for ((kb = 0; kb < 1024; kb += 4)); do \
+    echo "read -P 0 ${kb}k 1k"; \
+    echo "read -P 42 $((kb + 1))k 2k"; \
+    echo "read -P 0 $((kb + 3))k 1k"; \
+ done) \
+ | $QEMU_IO "$TEST_IMG" | _filter_qemu_io | grep 'verification'
+
+# Status of qemu-io
+if [ ${PIPESTATUS[1]} = 0 ]; then
+    echo 'Content verified.'
+fi
+
+# success, all done
+echo "*** done"
+rm -f $seq.full
+status=0
diff --git a/tests/qemu-iotests/265.out b/tests/qemu-iotests/265.out
new file mode 100644
index 0000000000..6eac620f25
--- /dev/null
+++ b/tests/qemu-iotests/265.out
@@ -0,0 +1,6 @@
+QA output created by 265
+--- Writing to the image ---
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
+--- Verifying its content ---
+Content verified.
+*** done
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index d95d556414..0c129c1644 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -274,3 +274,4 @@
 257 rw
 258 rw quick
 262 rw quick migration
+265 rw auto quick
-- 
2.21.0

Re: [Qemu-devel] [PATCH 0/2] block/file-posix: Fix xfs_write_zeroes()

[Paolo Bonzini]

On 22/08/19 18:26, Max Reitz wrote:
> Lukàš ran over a nasty regression in our xfs_write_zeroes() function
> (sorry, my fault) made apparent by a recent patch from Anton that makes
> qcow2 images heavily exercise the offending code path.
> 
> This series fixes the bug and adds a test to prevent it from
> reoccurring.
> 
> 
> Max Reitz (2):
>   block/file-posix: Fix xfs_write_zeroes()
>   iotests: Test reverse sub-cluster qcow2 writes
> 
>  block/file-posix.c         | 16 ++++++---
>  tests/qemu-iotests/265     | 67 ++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/265.out |  6 ++++
>  tests/qemu-iotests/group   |  1 +
>  4 files changed, 85 insertions(+), 5 deletions(-)
>  create mode 100755 tests/qemu-iotests/265
>  create mode 100644 tests/qemu-iotests/265.out
> 

What about just killing libxfs support and only use fallocate?
FALLOC_FL_ZERO_RANGE was added in Linux 3.15 (2014) and the only
platform we probably support with such an old kernel is of course
RHEL/CentOS 7 which has had it backported.

Paolo

Re: [Qemu-devel] [PATCH 0/2] block/file-posix: Fix xfs_write_zeroes()

[Max Reitz]

On 22.08.19 18:53, Paolo Bonzini wrote:
> On 22/08/19 18:26, Max Reitz wrote:
>> Lukàš ran over a nasty regression in our xfs_write_zeroes() function
>> (sorry, my fault) made apparent by a recent patch from Anton that makes
>> qcow2 images heavily exercise the offending code path.
>>
>> This series fixes the bug and adds a test to prevent it from
>> reoccurring.
>>
>>
>> Max Reitz (2):
>>   block/file-posix: Fix xfs_write_zeroes()
>>   iotests: Test reverse sub-cluster qcow2 writes
>>
>>  block/file-posix.c         | 16 ++++++---
>>  tests/qemu-iotests/265     | 67 ++++++++++++++++++++++++++++++++++++++
>>  tests/qemu-iotests/265.out |  6 ++++
>>  tests/qemu-iotests/group   |  1 +
>>  4 files changed, 85 insertions(+), 5 deletions(-)
>>  create mode 100755 tests/qemu-iotests/265
>>  create mode 100644 tests/qemu-iotests/265.out
>>
> 
> What about just killing libxfs support and only use fallocate?
> FALLOC_FL_ZERO_RANGE was added in Linux 3.15 (2014) and the only
> platform we probably support with such an old kernel is of course
> RHEL/CentOS 7 which has had it backported.

Works just as well for me. :-)

Max

Re: [Qemu-devel] [PATCH 0/2] block/file-posix: Fix xfs_write_zeroes()

[Lukáš Doktor]

[-- Attachment #1.1: Type: text/plain, Size: 1454 bytes --]

Dne 22. 08. 19 v 19:09 Max Reitz napsal(a):
> On 22.08.19 18:53, Paolo Bonzini wrote:
>> On 22/08/19 18:26, Max Reitz wrote:
>>> Lukàš ran over a nasty regression in our xfs_write_zeroes() function
>>> (sorry, my fault) made apparent by a recent patch from Anton that makes
>>> qcow2 images heavily exercise the offending code path.
>>>
>>> This series fixes the bug and adds a test to prevent it from
>>> reoccurring.
>>>
>>>
>>> Max Reitz (2):
>>>   block/file-posix: Fix xfs_write_zeroes()
>>>   iotests: Test reverse sub-cluster qcow2 writes
>>>
>>>  block/file-posix.c         | 16 ++++++---
>>>  tests/qemu-iotests/265     | 67 ++++++++++++++++++++++++++++++++++++++
>>>  tests/qemu-iotests/265.out |  6 ++++
>>>  tests/qemu-iotests/group   |  1 +
>>>  4 files changed, 85 insertions(+), 5 deletions(-)
>>>  create mode 100755 tests/qemu-iotests/265
>>>  create mode 100644 tests/qemu-iotests/265.out
>>>
>>
>> What about just killing libxfs support and only use fallocate?
>> FALLOC_FL_ZERO_RANGE was added in Linux 3.15 (2014) and the only
>> platform we probably support with such an old kernel is of course
>> RHEL/CentOS 7 which has had it backported.
> 
> Works just as well for me. :-)
> 
> Max
> 

Whatever you decide, anyway this patch fixes my arm installation issue and the attached qemu iotest is also passing on my system.

Thank you,
Lukáš

Tested-by: Lukáš Doktor <ldoktor@redhat.com>


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Re: [Qemu-devel] [PATCH 0/2] block/file-posix: Fix xfs_write_zeroes()

[Anton Nefedov]

On 22/8/2019 7:26 PM, Max Reitz wrote:
> Lukàš ran over a nasty regression in our xfs_write_zeroes() function
> (sorry, my fault) made apparent by a recent patch from Anton that makes
> qcow2 images heavily exercise the offending code path.
> 
> This series fixes the bug and adds a test to prevent it from
> reoccurring.
> 
> 
> Max Reitz (2):
>    block/file-posix: Fix xfs_write_zeroes()
>    iotests: Test reverse sub-cluster qcow2 writes
> 
>   block/file-posix.c         | 16 ++++++---
>   tests/qemu-iotests/265     | 67 ++++++++++++++++++++++++++++++++++++++
>   tests/qemu-iotests/265.out |  6 ++++
>   tests/qemu-iotests/group   |  1 +
>   4 files changed, 85 insertions(+), 5 deletions(-)
>   create mode 100755 tests/qemu-iotests/265
>   create mode 100644 tests/qemu-iotests/265.out
> 

Nice! thanks Max

Reviewed-by: Anton Nefedov <anton.nefedov@virtuozzo.com>