[PATCH v1] generic/563: tolerate small reads in "write -> read/write" sub-test

[bxue@redhat.com]

From: Boyang Xue <bxue@redhat.com>

On ext2/ext3, there're small reads when writing to file in the same cgroup.
Since this sub-test tests that if read/write from 2nd cgroup is both 0 after
writing in 1st cgroup, these small reads from 1st cgroup should not fail the
test. This patch fixes the sub-test in order to tolerate small reads in 1st
cgroup.

Signed-off-by: Boyang Xue <bxue@redhat.com>
---
Hi,

I found generic/563 fails on ext2/ext3 on the latest kernel:

[root@kvm109 repo_xfstests]# ./check generic/563
FSTYP         -- ext3
PLATFORM      -- Linux/x86_64 kvm109 5.12.0-0.rc3.170.xx.x86_64 #1 SMP Tue Mar
16 12:02:55 EDT 2021
MKFS_OPTIONS  -- -b 4096 /dev/vda3
MOUNT_OPTIONS -- -o rw,relatime,seclabel -o context=system_u:object_r:root_t:s0
/dev/vda3 /scratch

generic/563 4s ... - output mismatch (see
/tmp/tmp.hMWbgkavD4/repo_xfstests/results//generic/563.out.bad)
    --- tests/generic/563.out   2021-04-01 02:07:16.303329895 -0400
    +++ /tmp/tmp.hMWbgkavD4/repo_xfstests/results//generic/563.out.bad
2021-04-01 03:06:19.240329895 -0400
    @@ -3,7 +3,8 @@
     read is in range
     write is in range
     write -> read/write
    -read is in range
    +read has value of 12288
    +read is NOT in range 0 .. 0
     write is in range
    ...
    (Run 'diff -u /tmp/tmp.hMWbgkavD4/repo_xfstests/tests/generic/563.out
/tmp/tmp.hMWbgkavD4/repo_xfstests/results//generic/563.out.bad'  to see the
entire diff)
Ran: generic/563
Failures: generic/563
Failed 1 of 1 tests
```

generic/563 code
```
...
# Write from one cgroup then read and write from a second. Writes are charged to
# the first group and nothing to the second.
echo "write -> read/write"
reset  <== I have injected commands here for check, it turns out it indeed
resets rbytes and wbytes both to 0.
switch_cg $cgdir/$seq-cg
$XFS_IO_PROG -c "pwrite 0 $iosize" $SCRATCH_MNT/file >> $seqres.full 2>&1
switch_cg $cgdir/$seq-cg-2
$XFS_IO_PROG -c "pread 0 $iosize" -c "pwrite 0 $iosize" $SCRATCH_MNT/file \
	>> $seqres.full 2>&1
switch_cg $cgdir
$XFS_IO_PROG -c fsync $SCRATCH_MNT/file
check_cg $cgdir/$seq-cg 0 $iosize  <== problem here, expected read bytes = 0,
but it's 12288
check_cg $cgdir/$seq-cg-2 0 0
...
```

local.config
```
FSTYP="ext3"
TEST_DIR="/test"
TEST_DEV="/dev/vda2"
SCRATCH_MNT="/scratch"
SCRATCH_DEV="/dev/vda3"
LOGWRITES_MNT="/logwrites"
LOGWRITES_DEV="/dev/vda6"
MKFS_OPTIONS="-b 4096"
MOUNT_OPTIONS="-o rw,relatime,seclabel"
TEST_FS_MOUNT_OPTS="-o rw,relatime,seclabel"
```

I think the "write -> read/write" sub-test should test if the read/write bytes
in 2nd cgroup both are 0, after writing in the 1st cgroup. Given that it writes
8MB in cgroup, dozens of small reads in service of the write (like read
metadata) is not part of the goal of the sub-test, and should be tolerate,
rather than fail the test.

Currently, the expected read bytes in the 1st cgroup is strictly 0. This patch
sets a fixed tolerant value, so read bytes in the range of 0-(tolerant value) is
tolerant, doesn't fail the test.

I have run the original test on ext2/ext3/ext4 with 1k/2k/4k blksize on x86_64,
aarch64, s390x, ppc64le, to determine the tolerant value. It turns out the
maximum read bytes in the tests is 33792. So I think set the tolerant value
to 33800 is adequate.

Please help review this patch. Thanks.

-Boyang

 tests/generic/563 | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/tests/generic/563 b/tests/generic/563
index b113eacf..83146721 100755
--- a/tests/generic/563
+++ b/tests/generic/563
@@ -60,6 +60,8 @@ check_cg()
 	cgname=$(basename $cgroot)
 	expectedread=$2
 	expectedwrite=$3
+	readtol=$4
+	writetol=$5
 	rbytes=0
 	wbytes=0
 
@@ -71,8 +73,8 @@ check_cg()
 			awk -F = '{ print $2 }'`
 	fi
 
-	_within_tolerance "read" $rbytes $expectedread 5% -v
-	_within_tolerance "write" $wbytes $expectedwrite 5% -v
+	_within_tolerance "read" $rbytes $expectedread $readtol -v
+	_within_tolerance "write" $wbytes $expectedwrite $writetol -v
 }
 
 # Move current process to another cgroup.
@@ -113,7 +115,7 @@ $XFS_IO_PROG -c "pread 0 $iosize" -c "pwrite 0 $iosize" -c fsync \
 	$SCRATCH_MNT/file >> $seqres.full 2>&1
 switch_cg $cgdir
 $XFS_IO_PROG -c fsync $SCRATCH_MNT/file
-check_cg $cgdir/$seq-cg $iosize $iosize
+check_cg $cgdir/$seq-cg $iosize $iosize 5% 5%
 
 # Write from one cgroup then read and write from a second. Writes are charged to
 # the first group and nothing to the second.
@@ -126,8 +128,8 @@ $XFS_IO_PROG -c "pread 0 $iosize" -c "pwrite 0 $iosize" $SCRATCH_MNT/file \
 	>> $seqres.full 2>&1
 switch_cg $cgdir
 $XFS_IO_PROG -c fsync $SCRATCH_MNT/file
-check_cg $cgdir/$seq-cg 0 $iosize
-check_cg $cgdir/$seq-cg-2 0 0
+check_cg $cgdir/$seq-cg 0 $iosize 33800 5%
+check_cg $cgdir/$seq-cg-2 0 0 5% 5%
 
 # Read from one cgroup, read & write from a second. Both reads and writes are
 # charged to the first group and nothing to the second.
@@ -140,8 +142,8 @@ $XFS_IO_PROG -c "pread 0 $iosize" -c "pwrite 0 $iosize" $SCRATCH_MNT/file \
 	>> $seqres.full 2>&1
 switch_cg $cgdir
 $XFS_IO_PROG -c fsync $SCRATCH_MNT/file
-check_cg $cgdir/$seq-cg $iosize $iosize
-check_cg $cgdir/$seq-cg-2 0 0
+check_cg $cgdir/$seq-cg $iosize $iosize 5% 5%
+check_cg $cgdir/$seq-cg-2 0 0 5% 5%
 
 echo "-io" > $cgdir/cgroup.subtree_control || _fail "subtree control"
 
-- 
2.27.0