[PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

[PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

[Rajeev Mishra]

- Use vfs_getattr_nosec() instead of i_size_read() in lo_calculate_size.
- Improves accuracy for network/distributed filesystems.

Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
---
 drivers/block/loop.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 5faf8607dfb2..0a2703eda2c2 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -139,9 +139,20 @@ static int part_shift;
 
 static loff_t lo_calculate_size(struct loop_device *lo, struct file *file)
 {
+       struct kstat stat;
        loff_t loopsize;
-       /* Compute loopsize in bytes */
-       loopsize = i_size_read(file->f_mapping->host);
+       int ret;
+
+       /*
+	* Get the accurate file size. This provides better results than
+	* cached inode data, particularly for network filesystems where
+	* metadata may be stale.
+	*/
+       ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
+       if (ret)
+	       return 0;
+
+       loopsize = stat.size;
        if (lo->lo_offset > 0)
 	       loopsize -= lo->lo_offset;
        /* offset is beyond i_size, weird but possible */
-- 
2.43.7

[PATCH v4 1/2] loop: Rename and merge get_size/get_loop_size to lo_calculate_size

[Rajeev Mishra]

- Renamed get_size to lo_calculate_size.
- Merged get_size and get_loop_size logic into lo_calculate_size.
- Updated all callers to use lo_calculate_size.
- Added header to lo_calculate_size.

Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
---
 drivers/block/loop.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1b6ee91f8eb9..0e1b9eb9db10 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -137,20 +137,18 @@ static void loop_global_unlock(struct loop_device *lo, bool global)
 static int max_part;
 static int part_shift;
 
-static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
+static loff_t lo_calculate_size(struct loop_device *lo, struct file *file)
 {
 	loff_t loopsize;
-
 	/* Compute loopsize in bytes */
 	loopsize = i_size_read(file->f_mapping->host);
-	if (offset > 0)
-		loopsize -= offset;
+	if (lo->lo_offset > 0)
+		loopsize -= lo->lo_offset;
 	/* offset is beyond i_size, weird but possible */
 	if (loopsize < 0)
 		return 0;
-
-	if (sizelimit > 0 && sizelimit < loopsize)
-		loopsize = sizelimit;
+	if (lo->lo_sizelimit > 0 && lo->lo_sizelimit < loopsize)
+		loopsize = lo->lo_sizelimit;
 	/*
 	 * Unfortunately, if we want to do I/O on the device,
 	 * the number of 512-byte sectors has to fit into a sector_t.
@@ -158,11 +156,6 @@ static loff_t get_size(loff_t offset, loff_t sizelimit, struct file *file)
 	return loopsize >> 9;
 }
 
-static loff_t get_loop_size(struct loop_device *lo, struct file *file)
-{
-	return get_size(lo->lo_offset, lo->lo_sizelimit, file);
-}
-
 /*
  * We support direct I/O only if lo_offset is aligned with the logical I/O size
  * of backing device, and the logical block size of loop is bigger than that of
@@ -569,7 +562,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 	error = -EINVAL;
 
 	/* size of the new backing store needs to be the same */
-	if (get_loop_size(lo, file) != get_loop_size(lo, old_file))
+	if (lo_calculate_size(lo, file) != lo_calculate_size(lo, old_file))
 		goto out_err;
 
 	/*
@@ -1063,7 +1056,7 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
 	loop_update_dio(lo);
 	loop_sysfs_init(lo);
 
-	size = get_loop_size(lo, file);
+	size = lo_calculate_size(lo, file);
 	loop_set_size(lo, size);
 
 	/* Order wrt reading lo_state in loop_validate_file(). */
@@ -1255,8 +1248,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 	if (partscan)
 		clear_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state);
 	if (!err && size_changed) {
-		loff_t new_size = get_size(lo->lo_offset, lo->lo_sizelimit,
-					   lo->lo_backing_file);
+		loff_t new_size = lo_calculate_size(lo, lo->lo_backing_file);
 		loop_set_size(lo, new_size);
 	}
 out_unlock:
@@ -1399,7 +1391,7 @@ static int loop_set_capacity(struct loop_device *lo)
 	if (unlikely(lo->lo_state != Lo_bound))
 		return -ENXIO;
 
-	size = get_loop_size(lo, lo->lo_backing_file);
+	size = lo_calculate_size(lo, lo->lo_backing_file);
 	loop_set_size(lo, size);
 
 	return 0;
-- 
2.43.7

[PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

[Rajeev Mishra]

- Use vfs_getattr_nosec() instead of i_size_read() in lo_calculate_size.
- Improves accuracy for network/distributed filesystems.

Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
---
 drivers/block/loop.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 0e1b9eb9db10..57263c273f0f 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -139,9 +139,20 @@ static int part_shift;
 
 static loff_t lo_calculate_size(struct loop_device *lo, struct file *file)
 {
+	struct kstat stat;
 	loff_t loopsize;
-	/* Compute loopsize in bytes */
-	loopsize = i_size_read(file->f_mapping->host);
+	int ret;
+
+	/*
+	 * Get the accurate file size. This provides better results than
+	 * cached inode data, particularly for network filesystems where
+	 * metadata may be stale.
+	 */
+	ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
+	if (ret)
+		return 0;
+
+	loopsize = stat.size;
 	if (lo->lo_offset > 0)
 		loopsize -= lo->lo_offset;
 	/* offset is beyond i_size, weird but possible */
-- 
2.43.7

Re: [PATCH v4 1/2] loop: Rename and merge get_size/get_loop_size to lo_calculate_size

[Yu Kuai]

在 2025/08/15 3:10, Rajeev Mishra 写道:
> - Renamed get_size to lo_calculate_size.
> - Merged get_size and get_loop_size logic into lo_calculate_size.
> - Updated all callers to use lo_calculate_size.
> - Added header to lo_calculate_size.
> 
> Signed-off-by: Rajeev Mishra<rajeevm@hpe.com>
> ---
>   drivers/block/loop.c | 26 +++++++++-----------------
>   1 file changed, 9 insertions(+), 17 deletions(-)

LGTM
Reviewed-by: Yu Kuai <yukuai3@huawei.com>

Re: [PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

[Yu Kuai]

在 2025/08/15 3:10, Rajeev Mishra 写道:
> - Use vfs_getattr_nosec() instead of i_size_read() in lo_calculate_size.
> - Improves accuracy for network/distributed filesystems.
> 
> Signed-off-by: Rajeev Mishra<rajeevm@hpe.com>
> ---
>   drivers/block/loop.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)

LGTM
Reviewed-by: Yu Kuai <yukuai3@huawei.com>

Re: [PATCH v4 1/2] loop: Rename and merge get_size/get_loop_size to lo_calculate_size

[Jens Axboe]

On 8/14/25 1:10 PM, Rajeev Mishra wrote:
> - Renamed get_size to lo_calculate_size.
> - Merged get_size and get_loop_size logic into lo_calculate_size.
> - Updated all callers to use lo_calculate_size.
> - Added header to lo_calculate_size.

Please write a proper commit message, rather than these itemized
lists. Goes for both patches.

-- 
Jens Axboe

[PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

[Rajeev Mishra]

In lo_calculate_size, use vfs_getattr_nosec() instead of
i_size_read(), which improves accuracy for network and
distributed filesystems.

Signed-off-by: Rajeev Mishra <rajeevm@hpe.com>
---
 drivers/block/loop.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 0e1b9eb9db10..57263c273f0f 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -139,9 +139,20 @@ static int part_shift;
 
 static loff_t lo_calculate_size(struct loop_device *lo, struct file *file)
 {
+	struct kstat stat;
 	loff_t loopsize;
-	/* Compute loopsize in bytes */
-	loopsize = i_size_read(file->f_mapping->host);
+	int ret;
+
+	/*
+	 * Get the accurate file size. This provides better results than
+	 * cached inode data, particularly for network filesystems where
+	 * metadata may be stale.
+	 */
+	ret = vfs_getattr_nosec(&file->f_path, &stat, STATX_SIZE, 0);
+	if (ret)
+		return 0;
+
+	loopsize = stat.size;
 	if (lo->lo_offset > 0)
 		loopsize -= lo->lo_offset;
 	/* offset is beyond i_size, weird but possible */
-- 
2.43.7

Re: [PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

[kernel test robot]

Hello,

kernel test robot noticed "xfstests.generic.563.fail" on:

commit: fb455b8a6ac932603a8c0dbb787f8330b0924834 ("[PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size")
url: https://github.com/intel-lab-lkp/linux/commits/Rajeev-Mishra/loop-use-vfs_getattr_nosec-for-accurate-file-size/20250815-031401
base: https://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git for-next
patch link: https://lore.kernel.org/all/20250814191004.60340-2-rajeevm@hpe.com/
patch subject: [PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

in testcase: xfstests
version: xfstests-x86_64-e1e4a0ea-1_20250714
with following parameters:

	disk: 4HDD
	fs: ext4
	test: generic-563



config: x86_64-rhel-9.4-func
compiler: gcc-12
test machine: 4 threads Intel(R) Core(TM) i5-6500 CPU @ 3.20GHz (Skylake) with 32G memory

(please refer to attached dmesg/kmsg for entire log/backtrace)



If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <oliver.sang@intel.com>
| Closes: https://lore.kernel.org/oe-lkp/202508200409.b2459c02-lkp@intel.com

2025-08-17 21:02:18 export TEST_DIR=/fs/sda1
2025-08-17 21:02:18 export TEST_DEV=/dev/sda1
2025-08-17 21:02:18 export FSTYP=ext4
2025-08-17 21:02:18 export SCRATCH_MNT=/fs/scratch
2025-08-17 21:02:18 mkdir /fs/scratch -p
2025-08-17 21:02:18 export SCRATCH_DEV=/dev/sda4
2025-08-17 21:02:18 echo generic/563
2025-08-17 21:02:18 ./check -E tests/exclude/ext4 generic/563
FSTYP         -- ext4
PLATFORM      -- Linux/x86_64 lkp-skl-d03 6.17.0-rc1-00020-gfb455b8a6ac9 #1 SMP PREEMPT_DYNAMIC Mon Aug 18 03:05:49 CST 2025
MKFS_OPTIONS  -- -F /dev/sda4
MOUNT_OPTIONS -- -o acl,user_xattr /dev/sda4 /fs/scratch

generic/563       [failed, exit status 1]- output mismatch (see /lkp/benchmarks/xfstests/results//generic/563.out.bad)
    --- tests/generic/563.out	2025-07-14 17:48:52.000000000 +0000
    +++ /lkp/benchmarks/xfstests/results//generic/563.out.bad	2025-08-17 21:02:31.367411171 +0000
    @@ -1,14 +1 @@
     QA output created by 563
    -read/write
    -read is in range
    -write is in range
    -write -> read/write
    -read is in range
    -write is in range
    ...
    (Run 'diff -u /lkp/benchmarks/xfstests/tests/generic/563.out /lkp/benchmarks/xfstests/results//generic/563.out.bad'  to see the entire diff)
Ran: generic/563
Failures: generic/563
Failed 1 of 1 tests




The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20250820/202508200409.b2459c02-lkp@intel.com



-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size

[Yu Kuai]

Hi,

在 2025/08/20 12:55, kernel test robot 写道:
> 
> 
> Hello,
> 
> kernel test robot noticed "xfstests.generic.563.fail" on:
> 
> commit: fb455b8a6ac932603a8c0dbb787f8330b0924834 ("[PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size")
> url: https://github.com/intel-lab-lkp/linux/commits/Rajeev-Mishra/loop-use-vfs_getattr_nosec-for-accurate-file-size/20250815-031401
> base: https://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git for-next
> patch link: https://lore.kernel.org/all/20250814191004.60340-2-rajeevm@hpe.com/
> patch subject: [PATCH v4 2/2] loop: use vfs_getattr_nosec for accurate file size
> 
> in testcase: xfstests
> version: xfstests-x86_64-e1e4a0ea-1_20250714
> with following parameters:
> 
> 	disk: 4HDD
> 	fs: ext4
> 	test: generic-563
> 
> 
> 
> config: x86_64-rhel-9.4-func
> compiler: gcc-12
> test machine: 4 threads Intel(R) Core(TM) i5-6500 CPU @ 3.20GHz (Skylake) with 32G memory
> 
> (please refer to attached dmesg/kmsg for entire log/backtrace)
> 
> 
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <oliver.sang@intel.com>
> | Closes: https://lore.kernel.org/oe-lkp/202508200409.b2459c02-lkp@intel.com
> 
> 2025-08-17 21:02:18 export TEST_DIR=/fs/sda1
> 2025-08-17 21:02:18 export TEST_DEV=/dev/sda1
> 2025-08-17 21:02:18 export FSTYP=ext4
> 2025-08-17 21:02:18 export SCRATCH_MNT=/fs/scratch
> 2025-08-17 21:02:18 mkdir /fs/scratch -p
> 2025-08-17 21:02:18 export SCRATCH_DEV=/dev/sda4
> 2025-08-17 21:02:18 echo generic/563
> 2025-08-17 21:02:18 ./check -E tests/exclude/ext4 generic/563
> FSTYP         -- ext4
> PLATFORM      -- Linux/x86_64 lkp-skl-d03 6.17.0-rc1-00020-gfb455b8a6ac9 #1 SMP PREEMPT_DYNAMIC Mon Aug 18 03:05:49 CST 2025
> MKFS_OPTIONS  -- -F /dev/sda4
> MOUNT_OPTIONS -- -o acl,user_xattr /dev/sda4 /fs/scratch
> 
> generic/563       [failed, exit status 1]- output mismatch (see /lkp/benchmarks/xfstests/results//generic/563.out.bad)
>      --- tests/generic/563.out	2025-07-14 17:48:52.000000000 +0000
>      +++ /lkp/benchmarks/xfstests/results//generic/563.out.bad	2025-08-17 21:02:31.367411171 +0000
>      @@ -1,14 +1 @@
>       QA output created by 563
>      -read/write
>      -read is in range
>      -write is in range
>      -write -> read/write
>      -read is in range
>      -write is in range
>      ...
>      (Run 'diff -u /lkp/benchmarks/xfstests/tests/generic/563.out /lkp/benchmarks/xfstests/results//generic/563.out.bad'  to see the entire diff)
> Ran: generic/563
> Failures: generic/563
> Failed 1 of 1 tests
> 

This can be reporduce with just losetup /dev/loop0 /dev/sda, root cause
is that /dev/sda is from devtmpfs wherer the get_attr method for
is shmem_getattr, hence stat->size will be set to zero.

In vfs_getattr_nosec(), is the inode is block device, bdev_statx will be
called to override the result, however, STATX_SIZE is not handled here,
I feel handle STATX_SIZE in bdev_statx will make sense:

diff --git a/block/bdev.c b/block/bdev.c
index b77ddd12dc06..9672bb6ec4ad 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1324,6 +1324,9 @@ void bdev_statx(const struct path *path, struct 
kstat *stat, u32 request_mask)
         if (!bdev)
                 return;

+       if (request_mask & STATX_SIZE)
+               stat->size = bdev_nr_bytes(bdev);
+
         if (request_mask & STATX_DIOALIGN) {
                 stat->dio_mem_align = bdev_dma_alignment(bdev) + 1;
                 stat->dio_offset_align = bdev_logical_block_size(bdev);

Thanks,
Kuai

> 
> 
> 
> The kernel config and materials to reproduce are available at:
> https://download.01.org/0day-ci/archive/20250820/202508200409.b2459c02-lkp@intel.com
> 
> 
>