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Wong" To: Shiyang Ruan Cc: fstests@vger.kernel.org Subject: Re: [PATCH v3 15/17] generic: add race test between reflink and mmap read Message-ID: <20220111185516.GF31566@magnolia> References: <20211214081914.2478122-1-ruansy.fnst@fujitsu.com> <20211214081914.2478122-16-ruansy.fnst@fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211214081914.2478122-16-ruansy.fnst@fujitsu.com> Precedence: bulk List-ID: X-Mailing-List: fstests@vger.kernel.org On Tue, Dec 14, 2021 at 04:19:12PM +0800, Shiyang Ruan wrote: > Test for races or FS corruption between reflink and mmap reading the > target file. (MMAP version of generic/164,165) Hi, now that this test has been running for a couple of weeks, I have observed periodic false positives from this test: QA output created by 670 Format and mount Initialize files Reflink and mmap reread the files! 00001000: 61 61 61 61 61 61 61 61 62 62 62 62 62 62 62 62 aaaabbbb Finished reflinking I suspect that if the _mread_range of file3 races with the page cache invalidation that FICLONERANGE performs, it is possible that the mread dump will contain a mix of 0x61 and 0x62. Looking at mread_f, it looks like it does a byte-at-a-time copy of the mmap... if (rflag) { for (tmp = length - 1, c = 0; tmp >= 0; tmp--, c = 1) { *bp = *(((char *)mapping->addr) + dumpoffset + tmp); cnt++; ...which is a sufficient window for the page cache mapping to get invalidated such that the mread will block on the page fault until the reflink operation finishes. I think the solution here is to adjust the egrep regexp above to find any line that does /not/ contain a's or b's, since (in principle) the reflink could run fast enough that every byte read hits a pgae fault. What do you think? --D > Signed-off-by: Shiyang Ruan > --- > common/reflink | 11 +++++++ > tests/generic/913 | 72 +++++++++++++++++++++++++++++++++++++++++++ > tests/generic/913.out | 5 +++ > 3 files changed, 88 insertions(+) > create mode 100755 tests/generic/913 > create mode 100644 tests/generic/913.out > > diff --git a/common/reflink b/common/reflink > index 68dbdedd..455260c6 100644 > --- a/common/reflink > +++ b/common/reflink > @@ -186,6 +186,17 @@ _read_range() { > $XFS_IO_PROG $xfs_io_args -f -c "pread -q -v $offset $len" "$file" | cut -d ' ' -f '3-18' > } > > +# Prints a range of a file as a hex dump > +_mread_range() { > + file="$1" > + offset="$2" > + len="$3" > + xfs_io_args="$4" > + > + $XFS_IO_PROG $xfs_io_args -f -c "mmap -rw 0 $((offset + len))" \ > + -c "mread -v $offset $len" "$file" | cut -d ' ' -f '3-18' > +} > + > # Compare ranges of two files > _compare_range() { > file1="$1" > diff --git a/tests/generic/913 b/tests/generic/913 > new file mode 100755 > index 00000000..f709c36c > --- /dev/null > +++ b/tests/generic/913 > @@ -0,0 +1,72 @@ > +#! /bin/bash > +# SPDX-License-Identifier: GPL-2.0 > +# > +# FS QA Test No. 913 > +# > +# Test for races or FS corruption between reflink and mmap reading the > +# target file. (MMAP version of generic/164,165) > +# > +. ./common/preamble > +_begin_fstest auto clone > + > +_register_cleanup "_cleanup" BUS > + > +# Import common functions. > +. ./common/filter > +. ./common/reflink > + > +# real QA test starts here > +_require_scratch_reflink > +_require_cp_reflink > + > +echo "Format and mount" > +_scratch_mkfs > $seqres.full 2>&1 > +_scratch_mount >> $seqres.full 2>&1 > + > +testdir=$SCRATCH_MNT/test-$seq > +finished_file=/tmp/finished > +rm -rf $finished_file > +mkdir $testdir > + > +loops=512 > +nr_loops=$((loops - 1)) > +blksz=65536 > + > +echo "Initialize files" > +echo >> $seqres.full > +_pwrite_byte 0x61 0 $((loops * blksz)) $testdir/file1 >> $seqres.full > +_pwrite_byte 0x62 0 $((loops * blksz)) $testdir/file2 >> $seqres.full > +_cp_reflink $testdir/file1 $testdir/file3 > +_scratch_cycle_mount > + > +fbytes() { > + egrep -v '(61 61 61 61 61 61 61 61 61 61 61 61 61 61 61 61|62 62 62 62 62 62 62 62 62 62 62 62 62 62 62 62)' > +} > + > +reader() { > + while [ ! -e $finished_file ]; do > + _mread_range $testdir/file3 0 $((loops * blksz)) | fbytes > + done > +} > + > +echo "Reflink and mmap reread the files!" > +reader & > +for i in `seq 1 2`; do > + seq $nr_loops -1 0 | while read i; do > + _reflink_range $testdir/file1 $((i * blksz)) \ > + $testdir/file3 $((i * blksz)) $blksz >> $seqres.full > + [ $? -ne 0 ] && break > + done > + seq $nr_loops -1 0 | while read i; do > + _reflink_range $testdir/file2 $((i * blksz)) \ > + $testdir/file3 $((i * blksz)) $blksz >> $seqres.full > + [ $? -ne 0 ] && break > + done > +done > +echo "Finished reflinking" > +touch $finished_file > +wait > + > +# success, all done > +status=0 > +exit > diff --git a/tests/generic/913.out b/tests/generic/913.out > new file mode 100644 > index 00000000..a34df6ce > --- /dev/null > +++ b/tests/generic/913.out > @@ -0,0 +1,5 @@ > +QA output created by 913 > +Format and mount > +Initialize files > +Reflink and mmap reread the files! > +Finished reflinking > -- > 2.34.1 > > >