[PATCH v2] fstests: add a regression test for fiemap into an mmap range

[PATCH v2] fstests: add a regression test for fiemap into an mmap range

[Josef Bacik]

Btrfs had a deadlock that you could trigger by mmap'ing a large file and
using that as the buffer for fiemap.  This test adds a c program to do
this, and the fstest creates a large enough file and then runs the
reproducer on the file.  Without the fix btrfs deadlocks, with the fix
we pass fine.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
v1->v2:
- Add the fiemap group to the test.
- Actually include the reproducer helper program.

 src/Makefile          |  2 +-
 src/fiemap-fault.c    | 73 +++++++++++++++++++++++++++++++++++++++++++
 tests/generic/740     | 41 ++++++++++++++++++++++++
 tests/generic/740.out |  2 ++
 4 files changed, 117 insertions(+), 1 deletion(-)
 create mode 100644 src/fiemap-fault.c
 create mode 100644 tests/generic/740
 create mode 100644 tests/generic/740.out

diff --git a/src/Makefile b/src/Makefile
index d79015ce..916f6755 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -34,7 +34,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
 	attr_replace_test swapon mkswap t_attr_corruption t_open_tmpfiles \
 	fscrypt-crypt-util bulkstat_null_ocount splice-test chprojid_fail \
 	detached_mounts_propagation ext4_resize t_readdir_3 splice2pipe \
-	uuid_ioctl
+	uuid_ioctl fiemap-fault
 
 EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
 	      btrfs_crc32c_forged_name.py popdir.pl popattr.py \
diff --git a/src/fiemap-fault.c b/src/fiemap-fault.c
new file mode 100644
index 00000000..27081188
--- /dev/null
+++ b/src/fiemap-fault.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc.  All Rights Reserved.
+ */
+
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <linux/fs.h>
+#include <linux/types.h>
+#include <linux/fiemap.h>
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int prep_mmap_buffer(int fd, void **addr)
+{
+	struct stat st;
+	int ret;
+
+	ret = fstat(fd, &st);
+	if (ret)
+		err(1, "failed to stat %d", fd);
+
+	*addr = mmap(NULL, st.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+	if (*addr == MAP_FAILED)
+		err(1, "failed to mmap %d", fd);
+
+	return st.st_size;
+}
+
+int main(int argc, char *argv[])
+{
+	struct fiemap *fiemap;
+	size_t sz, last = 0;
+	void *buf = NULL;
+	int ret, fd;
+
+	if (argc != 2)
+		errx(1, "no in and out file name arguments given");
+
+	fd = open(argv[1], O_RDWR, 0666);
+	if (fd == -1)
+		err(1, "failed to open %s", argv[1]);
+
+	sz = prep_mmap_buffer(fd, &buf);
+
+	fiemap = (struct fiemap *)buf;
+	fiemap->fm_flags = 0;
+	fiemap->fm_extent_count = (sz - sizeof(struct fiemap)) /
+				  sizeof(struct fiemap_extent);
+
+	while (last < sz) {
+		int i;
+
+		fiemap->fm_start = last;
+		fiemap->fm_length = sz - last;
+
+		ret = ioctl(fd, FS_IOC_FIEMAP, (unsigned long)fiemap);
+		if (ret < 0)
+			err(1, "fiemap failed %d (%s)", errno, strerror(errno));
+		for (i = 0; i < fiemap->fm_mapped_extents; i++)
+		       last = fiemap->fm_extents[i].fe_logical +
+			       fiemap->fm_extents[i].fe_length;
+	}
+
+	close(fd);
+	return 0;
+}
diff --git a/tests/generic/740 b/tests/generic/740
new file mode 100644
index 00000000..30ace1dd
--- /dev/null
+++ b/tests/generic/740
@@ -0,0 +1,41 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2023 Meta Platforms, Inc.  All Rights Reserved.
+#
+# FS QA Test 708
+#
+# Test fiemap into an mmaped buffer of the same file
+#
+# Create a reasonably large file, then run a program which mmaps it and uses
+# that as a buffer for an fiemap call.  This is a regression test for btrfs
+# where we used to hold a lock for the duration of the fiemap call which would
+# result in a deadlock if we page faulted.
+#
+. ./common/preamble
+_begin_fstest quick auto fiemap
+[ $FSTYP == "btrfs" ] && \
+	_fixed_by_kernel_commit xxxxxxxxxxxx \
+		"btrfs: fix deadlock with fiemap and extent locking"
+
+# real QA test starts here
+_supported_fs generic
+_require_test
+_require_odirect
+_require_test_program fiemap-fault
+dst=$TEST_DIR/fiemap-fault-$seq
+
+echo "Silence is golden"
+
+for i in $(seq 0 2 1000)
+do
+	$XFS_IO_PROG -d -f -c "pwrite -q $((i * 4096)) 4096" $dst
+done
+
+$here/src/fiemap-fault $dst > /dev/null || _fail "failed doing fiemap"
+
+rm -f $dst
+
+# success, all done
+status=$?
+exit
+
diff --git a/tests/generic/740.out b/tests/generic/740.out
new file mode 100644
index 00000000..3f841e60
--- /dev/null
+++ b/tests/generic/740.out
@@ -0,0 +1,2 @@
+QA output created by 740
+Silence is golden
-- 
2.43.0

Re: [PATCH v2] fstests: add a regression test for fiemap into an mmap range

[Anand Jain]

On 2/12/24 22:11, Josef Bacik wrote:
> Btrfs had a deadlock that you could trigger by mmap'ing a large file and
> using that as the buffer for fiemap.  This test adds a c program to do
> this, and the fstest creates a large enough file and then runs the
> reproducer on the file.  Without the fix btrfs deadlocks, with the fix
> we pass fine.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
> v1->v2:
> - Add the fiemap group to the test.
> - Actually include the reproducer helper program.
> 
>   src/Makefile          |  2 +-
>   src/fiemap-fault.c    | 73 +++++++++++++++++++++++++++++++++++++++++++
>   tests/generic/740     | 41 ++++++++++++++++++++++++
>   tests/generic/740.out |  2 ++
>   4 files changed, 117 insertions(+), 1 deletion(-)
>   create mode 100644 src/fiemap-fault.c
>   create mode 100644 tests/generic/740
>   create mode 100644 tests/generic/740.out
> 
> diff --git a/src/Makefile b/src/Makefile
> index d79015ce..916f6755 100644
> --- a/src/Makefile
> +++ b/src/Makefile
> @@ -34,7 +34,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
>   	attr_replace_test swapon mkswap t_attr_corruption t_open_tmpfiles \
>   	fscrypt-crypt-util bulkstat_null_ocount splice-test chprojid_fail \
>   	detached_mounts_propagation ext4_resize t_readdir_3 splice2pipe \
> -	uuid_ioctl
> +	uuid_ioctl fiemap-fault
>   
>   EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
>   	      btrfs_crc32c_forged_name.py popdir.pl popattr.py \
> diff --git a/src/fiemap-fault.c b/src/fiemap-fault.c
> new file mode 100644
> index 00000000..27081188
> --- /dev/null
> +++ b/src/fiemap-fault.c


Pls add fiemap-fault file to .gitignore

more below.

> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2024 Meta Platforms, Inc.  All Rights Reserved.
> + */
> +
> +#include <sys/ioctl.h>
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <linux/fs.h>
> +#include <linux/types.h>
> +#include <linux/fiemap.h>
> +#include <err.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <unistd.h>
> +
> +int prep_mmap_buffer(int fd, void **addr)
> +{
> +	struct stat st;
> +	int ret;
> +
> +	ret = fstat(fd, &st);
> +	if (ret)
> +		err(1, "failed to stat %d", fd);
> +
> +	*addr = mmap(NULL, st.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
> +	if (*addr == MAP_FAILED)
> +		err(1, "failed to mmap %d", fd);
> +
> +	return st.st_size;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct fiemap *fiemap;
> +	size_t sz, last = 0;
> +	void *buf = NULL;
> +	int ret, fd;
> +
> +	if (argc != 2)
> +		errx(1, "no in and out file name arguments given");
> +
> +	fd = open(argv[1], O_RDWR, 0666);
> +	if (fd == -1)
> +		err(1, "failed to open %s", argv[1]);
> +
> +	sz = prep_mmap_buffer(fd, &buf);
> +
> +	fiemap = (struct fiemap *)buf;
> +	fiemap->fm_flags = 0;
> +	fiemap->fm_extent_count = (sz - sizeof(struct fiemap)) /
> +				  sizeof(struct fiemap_extent);
> +
> +	while (last < sz) {
> +		int i;
> +
> +		fiemap->fm_start = last;
> +		fiemap->fm_length = sz - last;
> +
> +		ret = ioctl(fd, FS_IOC_FIEMAP, (unsigned long)fiemap);
> +		if (ret < 0)
> +			err(1, "fiemap failed %d (%s)", errno, strerror(errno));
> +		for (i = 0; i < fiemap->fm_mapped_extents; i++)
> +		       last = fiemap->fm_extents[i].fe_logical +
> +			       fiemap->fm_extents[i].fe_length;
> +	}
> +

   munmap() is missing.
   a few more below.

> +	close(fd);
> +	return 0;
> +}
> diff --git a/tests/generic/740 b/tests/generic/740
> new file mode 100644
> index 00000000..30ace1dd
> --- /dev/null
> +++ b/tests/generic/740
> @@ -0,0 +1,41 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2023 Meta Platforms, Inc.  All Rights Reserved.
> +#
> +# FS QA Test 708
> +#
> +# Test fiemap into an mmaped buffer of the same file
> +#
> +# Create a reasonably large file, then run a program which mmaps it and uses
> +# that as a buffer for an fiemap call.  This is a regression test for btrfs
> +# where we used to hold a lock for the duration of the fiemap call which would
> +# result in a deadlock if we page faulted.
> +#
> +. ./common/preamble
> +_begin_fstest quick auto fiemap
> +[ $FSTYP == "btrfs" ] && \
> +	_fixed_by_kernel_commit xxxxxxxxxxxx \
> +		"btrfs: fix deadlock with fiemap and extent locking"
> +
> +# real QA test starts here
> +_supported_fs generic
> +_require_test
> +_require_odirect
> +_require_test_program fiemap-fault
> +dst=$TEST_DIR/fiemap-fault-$seq

  Could we pls use:
    dst=$TEST_DIR/$seq/fiemap-fault
    mkdir -p $dst

  Keeps $TEST_DIR organized.

> +
> +echo "Silence is golden"
> +
> +for i in $(seq 0 2 1000)
> +do
> +	$XFS_IO_PROG -d -f -c "pwrite -q $((i * 4096)) 4096" $dst
> +done
> +
> +$here/src/fiemap-fault $dst > /dev/null || _fail "failed doing fiemap"
> +


> +rm -f $dst

Pls move this to custom clean up at _cleanup() within the testcase.

Thanks, Anand



> +
> +# success, all done
> +status=$?
> +exit
> +
> diff --git a/tests/generic/740.out b/tests/generic/740.out
> new file mode 100644
> index 00000000..3f841e60
> --- /dev/null
> +++ b/tests/generic/740.out
> @@ -0,0 +1,2 @@
> +QA output created by 740
> +Silence is golden

Re: [PATCH v2] fstests: add a regression test for fiemap into an mmap range

[David Disseldorp]

On Mon, 12 Feb 2024 11:41:14 -0500, Josef Bacik wrote:

> Btrfs had a deadlock that you could trigger by mmap'ing a large file and
> using that as the buffer for fiemap.  This test adds a c program to do
> this, and the fstest creates a large enough file and then runs the
> reproducer on the file.  Without the fix btrfs deadlocks, with the fix
> we pass fine.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

With a .gitignore entry added for the fiemap-fault binary:
Revewed-by: David Disseldorp <ddiss@suse.de>

A few other minor nits below...

> ---
> v1->v2:
> - Add the fiemap group to the test.
> - Actually include the reproducer helper program.
> 
>  src/Makefile          |  2 +-
>  src/fiemap-fault.c    | 73 +++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/740     | 41 ++++++++++++++++++++++++
>  tests/generic/740.out |  2 ++
>  4 files changed, 117 insertions(+), 1 deletion(-)
>  create mode 100644 src/fiemap-fault.c
>  create mode 100644 tests/generic/740
>  create mode 100644 tests/generic/740.out
> 
> diff --git a/src/Makefile b/src/Makefile
> index d79015ce..916f6755 100644
> --- a/src/Makefile
> +++ b/src/Makefile
> @@ -34,7 +34,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
>  	attr_replace_test swapon mkswap t_attr_corruption t_open_tmpfiles \
>  	fscrypt-crypt-util bulkstat_null_ocount splice-test chprojid_fail \
>  	detached_mounts_propagation ext4_resize t_readdir_3 splice2pipe \
> -	uuid_ioctl
> +	uuid_ioctl fiemap-fault

Nit: FWIW, this hunk collides with 3a0381a4 ("btrfs: test snapshotting a
deleted subvolume")

>  EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
>  	      btrfs_crc32c_forged_name.py popdir.pl popattr.py \
> diff --git a/src/fiemap-fault.c b/src/fiemap-fault.c
> new file mode 100644
> index 00000000..27081188
> --- /dev/null
> +++ b/src/fiemap-fault.c
> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2024 Meta Platforms, Inc.  All Rights Reserved.
> + */
> +
> +#include <sys/ioctl.h>
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <linux/fs.h>
> +#include <linux/types.h>
> +#include <linux/fiemap.h>
> +#include <err.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <unistd.h>
> +
> +int prep_mmap_buffer(int fd, void **addr)
> +{
> +	struct stat st;
> +	int ret;
> +
> +	ret = fstat(fd, &st);
> +	if (ret)
> +		err(1, "failed to stat %d", fd);
> +
> +	*addr = mmap(NULL, st.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
> +	if (*addr == MAP_FAILED)
> +		err(1, "failed to mmap %d", fd);
> +
> +	return st.st_size;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct fiemap *fiemap;
> +	size_t sz, last = 0;
> +	void *buf = NULL;
> +	int ret, fd;
> +
> +	if (argc != 2)
> +		errx(1, "no in and out file name arguments given");
> +
> +	fd = open(argv[1], O_RDWR, 0666);
> +	if (fd == -1)
> +		err(1, "failed to open %s", argv[1]);
> +
> +	sz = prep_mmap_buffer(fd, &buf);
> +
> +	fiemap = (struct fiemap *)buf;
> +	fiemap->fm_flags = 0;
> +	fiemap->fm_extent_count = (sz - sizeof(struct fiemap)) /
> +				  sizeof(struct fiemap_extent);
> +
> +	while (last < sz) {
> +		int i;
> +
> +		fiemap->fm_start = last;
> +		fiemap->fm_length = sz - last;
> +
> +		ret = ioctl(fd, FS_IOC_FIEMAP, (unsigned long)fiemap);
> +		if (ret < 0)
> +			err(1, "fiemap failed %d (%s)", errno, strerror(errno));

Nit: err() should already append the strerror() string.

> +		for (i = 0; i < fiemap->fm_mapped_extents; i++)
> +		       last = fiemap->fm_extents[i].fe_logical +
> +			       fiemap->fm_extents[i].fe_length;
> +	}
> +
> +	close(fd);
> +	return 0;
> +}
> diff --git a/tests/generic/740 b/tests/generic/740
> new file mode 100644
> index 00000000..30ace1dd
> --- /dev/null
> +++ b/tests/generic/740
> @@ -0,0 +1,41 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2023 Meta Platforms, Inc.  All Rights Reserved.
> +#
> +# FS QA Test 708

Test 740

> +#
> +# Test fiemap into an mmaped buffer of the same file
> +#
> +# Create a reasonably large file, then run a program which mmaps it and uses
> +# that as a buffer for an fiemap call.  This is a regression test for btrfs
> +# where we used to hold a lock for the duration of the fiemap call which would
> +# result in a deadlock if we page faulted.
> +#
> +. ./common/preamble
> +_begin_fstest quick auto fiemap
> +[ $FSTYP == "btrfs" ] && \
> +	_fixed_by_kernel_commit xxxxxxxxxxxx \
> +		"btrfs: fix deadlock with fiemap and extent locking"
> +
> +# real QA test starts here
> +_supported_fs generic
> +_require_test
> +_require_odirect
> +_require_test_program fiemap-fault
> +dst=$TEST_DIR/fiemap-fault-$seq
> +
> +echo "Silence is golden"
> +
> +for i in $(seq 0 2 1000)
> +do
> +	$XFS_IO_PROG -d -f -c "pwrite -q $((i * 4096)) 4096" $dst
> +done
> +
> +$here/src/fiemap-fault $dst > /dev/null || _fail "failed doing fiemap"

Nit: the error paths print errors, so the explicit _fail should be
unnecessary, or you could turn it into an echo.

> +
> +rm -f $dst
> +
> +# success, all done
> +status=$?
> +exit
> +
> diff --git a/tests/generic/740.out b/tests/generic/740.out
> new file mode 100644
> index 00000000..3f841e60
> --- /dev/null
> +++ b/tests/generic/740.out
> @@ -0,0 +1,2 @@
> +QA output created by 740
> +Silence is golden

Re: [PATCH v2] fstests: add a regression test for fiemap into an mmap range

[Zorro Lang]

On Mon, Feb 12, 2024 at 11:41:14AM -0500, Josef Bacik wrote:
> Btrfs had a deadlock that you could trigger by mmap'ing a large file and
> using that as the buffer for fiemap.  This test adds a c program to do
> this, and the fstest creates a large enough file and then runs the
> reproducer on the file.  Without the fix btrfs deadlocks, with the fix
> we pass fine.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
> v1->v2:
> - Add the fiemap group to the test.
> - Actually include the reproducer helper program.

Looks like this patch is missed (except the author changed the patch subject:),
correct me if I'm wrong. The last review point hoped to add "src/fiemap-fault"
to .gitignore.

> 
>  src/Makefile          |  2 +-
>  src/fiemap-fault.c    | 73 +++++++++++++++++++++++++++++++++++++++++++
>  tests/generic/740     | 41 ++++++++++++++++++++++++
>  tests/generic/740.out |  2 ++
>  4 files changed, 117 insertions(+), 1 deletion(-)
>  create mode 100644 src/fiemap-fault.c
>  create mode 100644 tests/generic/740
>  create mode 100644 tests/generic/740.out
> 

[snip]

> diff --git a/tests/generic/740 b/tests/generic/740
> new file mode 100644
> index 00000000..30ace1dd
> --- /dev/null
> +++ b/tests/generic/740
> @@ -0,0 +1,41 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2023 Meta Platforms, Inc.  All Rights Reserved.
> +#
> +# FS QA Test 708
> +#
> +# Test fiemap into an mmaped buffer of the same file
> +#
> +# Create a reasonably large file, then run a program which mmaps it and uses
> +# that as a buffer for an fiemap call.  This is a regression test for btrfs
> +# where we used to hold a lock for the duration of the fiemap call which would
> +# result in a deadlock if we page faulted.
> +#
> +. ./common/preamble
> +_begin_fstest quick auto fiemap
> +[ $FSTYP == "btrfs" ] && \
> +	_fixed_by_kernel_commit xxxxxxxxxxxx \

This commit id is "b0ad381fa769" now.

> +		"btrfs: fix deadlock with fiemap and extent locking"
> +
> +# real QA test starts here
> +_supported_fs generic
> +_require_test
> +_require_odirect
> +_require_test_program fiemap-fault
> +dst=$TEST_DIR/fiemap-fault-$seq
> +
> +echo "Silence is golden"
> +
> +for i in $(seq 0 2 1000)
> +do
> +	$XFS_IO_PROG -d -f -c "pwrite -q $((i * 4096)) 4096" $dst
> +done

_require_sparse_files ?

> +
> +$here/src/fiemap-fault $dst > /dev/null || _fail "failed doing fiemap"
> +
> +rm -f $dst

If you'd like to remove this file, do it in _cleanup(), e.g.

_cleanup()
{
	rm -f $dst
	cd /
	rm -r -f $tmp.*
}

Could you rebase this patch on latest fstests for-next branch with above
changes, then send a V2 please? I'd like to have this patch in next fstests
release.

Thanks,
Zorro

> +
> +# success, all done
> +status=$?
> +exit
> +
> diff --git a/tests/generic/740.out b/tests/generic/740.out
> new file mode 100644
> index 00000000..3f841e60
> --- /dev/null
> +++ b/tests/generic/740.out
> @@ -0,0 +1,2 @@
> +QA output created by 740
> +Silence is golden
> -- 
> 2.43.0
> 
> 

Re: [PATCH v2] fstests: add a regression test for fiemap into an mmap range

[Josef Bacik]

On Wed, Mar 13, 2024 at 11:48:51PM +0800, Zorro Lang wrote:
> On Mon, Feb 12, 2024 at 11:41:14AM -0500, Josef Bacik wrote:
> > Btrfs had a deadlock that you could trigger by mmap'ing a large file and
> > using that as the buffer for fiemap.  This test adds a c program to do
> > this, and the fstest creates a large enough file and then runs the
> > reproducer on the file.  Without the fix btrfs deadlocks, with the fix
> > we pass fine.
> > 
> > Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> > ---
> > v1->v2:
> > - Add the fiemap group to the test.
> > - Actually include the reproducer helper program.
> 
> Looks like this patch is missed (except the author changed the patch subject:),
> correct me if I'm wrong. The last review point hoped to add "src/fiemap-fault"
> to .gitignore.
> 
> > 
> >  src/Makefile          |  2 +-
> >  src/fiemap-fault.c    | 73 +++++++++++++++++++++++++++++++++++++++++++
> >  tests/generic/740     | 41 ++++++++++++++++++++++++
> >  tests/generic/740.out |  2 ++
> >  4 files changed, 117 insertions(+), 1 deletion(-)
> >  create mode 100644 src/fiemap-fault.c
> >  create mode 100644 tests/generic/740
> >  create mode 100644 tests/generic/740.out
> > 
> 
> [snip]
> 
> > diff --git a/tests/generic/740 b/tests/generic/740
> > new file mode 100644
> > index 00000000..30ace1dd
> > --- /dev/null
> > +++ b/tests/generic/740
> > @@ -0,0 +1,41 @@
> > +#! /bin/bash
> > +# SPDX-License-Identifier: GPL-2.0
> > +# Copyright (c) 2023 Meta Platforms, Inc.  All Rights Reserved.
> > +#
> > +# FS QA Test 708
> > +#
> > +# Test fiemap into an mmaped buffer of the same file
> > +#
> > +# Create a reasonably large file, then run a program which mmaps it and uses
> > +# that as a buffer for an fiemap call.  This is a regression test for btrfs
> > +# where we used to hold a lock for the duration of the fiemap call which would
> > +# result in a deadlock if we page faulted.
> > +#
> > +. ./common/preamble
> > +_begin_fstest quick auto fiemap
> > +[ $FSTYP == "btrfs" ] && \
> > +	_fixed_by_kernel_commit xxxxxxxxxxxx \
> 
> This commit id is "b0ad381fa769" now.
> 
> > +		"btrfs: fix deadlock with fiemap and extent locking"
> > +
> > +# real QA test starts here
> > +_supported_fs generic
> > +_require_test
> > +_require_odirect
> > +_require_test_program fiemap-fault
> > +dst=$TEST_DIR/fiemap-fault-$seq
> > +
> > +echo "Silence is golden"
> > +
> > +for i in $(seq 0 2 1000)
> > +do
> > +	$XFS_IO_PROG -d -f -c "pwrite -q $((i * 4096)) 4096" $dst
> > +done
> 
> _require_sparse_files ?
> 

This is the only comment I didn't incorporate, I'm not looking for sparse files,
I'm just looking for a lot of extents.  If smb fills in the holes I suppose this
will only be a problem if it fills them in contiguously, but it'll just create a
4gib file instead of a 2gib file.  Thanks,

Josef