On Mon, Apr 15, 2024 at 01:10:54AM -0700, Luis Chamberlain wrote:
> mmap() POSIX compliance says we should zero fill data beyond a file
> size up to page boundary, and issue a SIGBUS if we go beyond. While fsx
> helps us test zero-fill sometimes, fsstress also let's us sometimes test
> for SIGBUS however that is based on a random value and its not likley we
> always test it. Dedicate a specic test for this to make testing for
> this specific situation and to easily expand on other corner cases.
>
> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> ---
>
> Does enough to get us to use to test this, however I'm aware of a bit
> more polishing up to do:
>
> * maybe moving mread to common as generic/574 did it first
> * sharing round_up_to_page_boundary() as well
>
> generic/574 is special, it was just testing for correctness of
> integrity if we muck with mmap() however if you don't have verity
> stuff available obviously you won't end up testing it.
>
> This generalizes mmap() zero-fill and SIGBUS corner case tests.
>
> I've tested so far only 4k and it works well there. For 16k bs on LBS
> just the SIGBUS issue exists, I'll test smaller block sizes later like
> 512, 1k, 2k as well. We'll fix triggering the SIBGUS when LBS is used,
> we'll address that in the next iteration.
>
> Is this a worthy test as a generic test?
>
> common/filter | 6 ++
> tests/generic/740 | 231 ++++++++++++++++++++++++++++++++++++++++++
> tests/generic/740.out | 2 +
> 3 files changed, 239 insertions(+)
> create mode 100755 tests/generic/740
> create mode 100644 tests/generic/740.out
>
We could also extend the test to include mmap writes.
I took the lazy approach here but I think we can make the code look
prettier by adding some more functions that can do both mmap read and writes.
diff --git a/tests/generic/740 b/tests/generic/740
index cbb82301..93663964 100755
--- a/tests/generic/740
+++ b/tests/generic/740
@@ -53,6 +53,25 @@ round_up_to_page_boundary()
echo $(( (n + page_size - 1) & ~(page_size - 1) ))
}
+mwrite()
+{
+ local file=$1
+ local map_len=$2
+ local offset=$3
+ local length=$4
+
+ # Some callers expect xfs_io to crash with SIGBUS due to the mread,
+ # causing the shell to print "Bus error" to stderr. To allow this
+ # message to be redirected, execute xfs_io in a new shell instance.
+ # However, for this to work reliably, we also need to prevent the new
+ # shell instance from optimizing out the fork and directly exec'ing
+ # xfs_io. The easiest way to do that is to append 'true' to the
+ # commands, so that xfs_io is no longer the last command the shell sees.
+ bash -c "trap '' SIGBUS; $XFS_IO_PROG $file \
+ -c 'mmap -w 0 $map_len' \
+ -c 'mwrite $offset $length'; true"
+}
+
mread()
{
local file=$1
@@ -180,6 +199,12 @@ do_mmap_tests()
_fail
fi
+ # This should just work
+ mwrite $test_file $map_len 0 $map_len >> $seqres.full 2>$tmp.err
+ if [[ $? -ne 0 ]]; then
+ _fail
+ fi
+
# If we mmap() on the boundary but try to read beyond it just
# fails, we don't get a SIGBUS
$XFS_IO_PROG -r $test_file \
@@ -192,12 +217,29 @@ do_mmap_tests()
_fail
fi
+ $XFS_IO_PROG -w $test_file \
+ -c "mmap -w 0 $map_len" \
+ -c "mwrite 0 $((map_len + 10))" >> $seqres.full 2>$tmp.err
+ local mwrite_err=$?
+ if [[ $mwrite_err -eq 0 ]]; then
+ echo "mmap() to page boundary works as expected but writing beyond should fail"
+ echo "err: $?"
+ _fail
+ fi
+
# Now let's go beyond the allowed mmap() page boundary
mread $test_file $((map_len + 10)) 0 $((map_len + 10)) >> $seqres.full 2>$tmp.err
if ! grep -q 'Bus error' $tmp.err; then
echo "Expected SIGBUS when mmap() reading beyond page boundary"
_fail
fi
+
+ mwrite $test_file $((map_len + 10)) 0 $((map_len + 10)) >> $seqres.full 2>$tmp.err
+ if ! grep -q 'Bus error' $tmp.err; then
+ echo "Expected SIGBUS when mmap() writing beyond page boundary"
+ _fail
+ fi
+
local filelen_test=$(_get_filesize $test_file)
if [[ "$filelen_test" != "$new_filelen" ]]; then
echo "Expected file length: $new_filelen"
--
Pankaj
