linux-toradex.git/fs/cachefiles, branch v5.19-rc8 Linux kernel for Apalis and Colibri modules cachefiles: narrow the scope of flushed requests when releasing fd 2022-07-05T15:12:21+00:00 Jia Zhu zhujia.zj@bytedance.com 2022-06-09T08:54:10+00:00 65aa5f6fd8a12e0a343aaf1815949a79a49e3f35 When an anonymous fd is released, only flush the requests associated with it, rather than all of requests in xarray. Fixes: 9032b6e8589f ("cachefiles: implement on-demand read") Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeffle Xu <jefflexu@linux.alibaba.com> Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com> Link: https://listman.redhat.com/archives/linux-cachefs/2022-June/006937.html 
When an anonymous fd is released, only flush the requests
associated with it, rather than all of requests in xarray.

Fixes: 9032b6e8589f ("cachefiles: implement on-demand read")
Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://listman.redhat.com/archives/linux-cachefs/2022-June/006937.html
cachefiles: add tracepoints for on-demand read mode 2022-05-17T16:11:18+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-04-25T12:21:29+00:00 1519670e4fecc6063fa2f0c10f0666d3331f219b Add tracepoints for on-demand read mode. Currently following tracepoints are added: OPEN request / COPEN reply CLOSE request READ request / CREAD reply write through anonymous fd release of anonymous fd Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Acked-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/20220425122143.56815-8-jefflexu@linux.alibaba.com Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> 
Add tracepoints for on-demand read mode. Currently following tracepoints
are added:

	OPEN request / COPEN reply
	CLOSE request
	READ request / CREAD reply
	write through anonymous fd
	release of anonymous fd

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20220425122143.56815-8-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
cachefiles: enable on-demand read mode 2022-05-17T16:11:18+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-04-25T12:21:28+00:00 4e4f1788af0e477bca079e5b1ffc42846b3bafee Enable on-demand read mode by adding an optional parameter to the "bind" command. On-demand mode will be turned on when this parameter is "ondemand", i.e. "bind ondemand". Otherwise cachefiles will work in the original mode. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Link: https://lore.kernel.org/r/20220509074028.74954-7-jefflexu@linux.alibaba.com Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> 
Enable on-demand read mode by adding an optional parameter to the "bind"
command.

On-demand mode will be turned on when this parameter is "ondemand", i.e.
"bind ondemand". Otherwise cachefiles will work in the original mode.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220509074028.74954-7-jefflexu@linux.alibaba.com
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
cachefiles: implement on-demand read 2022-05-17T16:11:18+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-04-25T12:21:27+00:00 9032b6e8589f269743984aac53e82e4835be16dc Implement the data plane of on-demand read mode. The early implementation [1] place the entry to cachefiles_ondemand_read() in fscache_read(). However, fscache_read() can only detect if the requested file range is fully cache miss, whilst we need to notify the user daemon as long as there's a hole inside the requested file range. Thus the entry is now placed in cachefiles_prepare_read(). When working in on-demand read mode, once a hole detected, the read routine will send a READ request to the user daemon. The user daemon needs to fetch the data and write it to the cache file. After sending the READ request, the read routine will hang there, until the READ request is handled by the user daemon. Then it will retry to read from the same file range. If no progress encountered, the read routine will fail then. A new NETFS_SREQ_ONDEMAND flag is introduced to indicate that on-demand read should be done when a cache miss encountered. [1] https://lore.kernel.org/all/20220406075612.60298-6-jefflexu@linux.alibaba.com/ #v8 Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Acked-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/20220425122143.56815-6-jefflexu@linux.alibaba.com Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> 
Implement the data plane of on-demand read mode.

The early implementation [1] place the entry to
cachefiles_ondemand_read() in fscache_read(). However, fscache_read()
can only detect if the requested file range is fully cache miss, whilst
we need to notify the user daemon as long as there's a hole inside the
requested file range.

Thus the entry is now placed in cachefiles_prepare_read(). When working
in on-demand read mode, once a hole detected, the read routine will send
a READ request to the user daemon. The user daemon needs to fetch the
data and write it to the cache file. After sending the READ request, the
read routine will hang there, until the READ request is handled by the
user daemon. Then it will retry to read from the same file range. If no
progress encountered, the read routine will fail then.

A new NETFS_SREQ_ONDEMAND flag is introduced to indicate that on-demand
read should be done when a cache miss encountered.

[1] https://lore.kernel.org/all/20220406075612.60298-6-jefflexu@linux.alibaba.com/ #v8

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20220425122143.56815-6-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
cachefiles: notify the user daemon when withdrawing cookie 2022-05-17T16:11:17+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-04-25T12:21:26+00:00 324b954ac80cff0d11ddb6bde9b6631e45e98620 Notify the user daemon that cookie is going to be withdrawn, providing a hint that the associated anonymous fd can be closed. Be noted that this is only a hint. The user daemon may close the associated anonymous fd when receiving the CLOSE request, then it will receive another anonymous fd when the cookie gets looked up. Or it may ignore the CLOSE request, and keep writing data through the anonymous fd. However the next time the cookie gets looked up, the user daemon will still receive another new anonymous fd. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Acked-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/20220425122143.56815-5-jefflexu@linux.alibaba.com Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> 
Notify the user daemon that cookie is going to be withdrawn, providing a
hint that the associated anonymous fd can be closed.

Be noted that this is only a hint. The user daemon may close the
associated anonymous fd when receiving the CLOSE request, then it will
receive another anonymous fd when the cookie gets looked up. Or it may
ignore the CLOSE request, and keep writing data through the anonymous
fd. However the next time the cookie gets looked up, the user daemon
will still receive another new anonymous fd.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20220425122143.56815-5-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
cachefiles: unbind cachefiles gracefully in on-demand mode 2022-05-17T16:11:17+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-04-25T12:21:25+00:00 d11b0b043b4008d64abaf1a26eea3dbcd906ee59 Add a refcount to avoid the deadlock in on-demand read mode. The on-demand read mode will pin the corresponding cachefiles object for each anonymous fd. The cachefiles object is unpinned when the anonymous fd gets closed. When the user daemon exits and the fd of "/dev/cachefiles" device node gets closed, it will wait for all cahcefiles objects getting withdrawn. Then if there's any anonymous fd getting closed after the fd of the device node, the user daemon will hang forever, waiting for all objects getting withdrawn. To fix this, add a refcount indicating if there's any object pinned by anonymous fds. The cachefiles cache gets unbound and withdrawn when the refcount is decreased to 0. It won't change the behaviour of the original mode, in which case the cachefiles cache gets unbound and withdrawn as long as the fd of the device node gets closed. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Link: https://lore.kernel.org/r/20220509074028.74954-4-jefflexu@linux.alibaba.com Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> 
Add a refcount to avoid the deadlock in on-demand read mode. The
on-demand read mode will pin the corresponding cachefiles object for
each anonymous fd. The cachefiles object is unpinned when the anonymous
fd gets closed. When the user daemon exits and the fd of
"/dev/cachefiles" device node gets closed, it will wait for all
cahcefiles objects getting withdrawn. Then if there's any anonymous fd
getting closed after the fd of the device node, the user daemon will
hang forever, waiting for all objects getting withdrawn.

To fix this, add a refcount indicating if there's any object pinned by
anonymous fds. The cachefiles cache gets unbound and withdrawn when the
refcount is decreased to 0. It won't change the behaviour of the
original mode, in which case the cachefiles cache gets unbound and
withdrawn as long as the fd of the device node gets closed.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220509074028.74954-4-jefflexu@linux.alibaba.com
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
cachefiles: notify the user daemon when looking up cookie 2022-05-17T16:11:17+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-04-25T12:21:24+00:00 c8383054506c77b814489c09877b5db83fd4abf2 Fscache/CacheFiles used to serve as a local cache for a remote networking fs. A new on-demand read mode will be introduced for CacheFiles, which can boost the scenario where on-demand read semantics are needed, e.g. container image distribution. The essential difference between these two modes is seen when a cache miss occurs: In the original mode, the netfs will fetch the data from the remote server and then write it to the cache file; in on-demand read mode, fetching the data and writing it into the cache is delegated to a user daemon. As the first step, notify the user daemon when looking up cookie. In this case, an anonymous fd is sent to the user daemon, through which the user daemon can write the fetched data to the cache file. Since the user daemon may move the anonymous fd around, e.g. through dup(), an object ID uniquely identifying the cache file is also attached. Also add one advisory flag (FSCACHE_ADV_WANT_CACHE_SIZE) suggesting that the cache file size shall be retrieved at runtime. This helps the scenario where one cache file contains multiple netfs files, e.g. for the purpose of deduplication. In this case, netfs itself has no idea the size of the cache file, whilst the user daemon should give the hint on it. Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Link: https://lore.kernel.org/r/20220509074028.74954-3-jefflexu@linux.alibaba.com Acked-by: David Howells <dhowells@redhat.com> Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> 
Fscache/CacheFiles used to serve as a local cache for a remote
networking fs. A new on-demand read mode will be introduced for
CacheFiles, which can boost the scenario where on-demand read semantics
are needed, e.g. container image distribution.

The essential difference between these two modes is seen when a cache
miss occurs: In the original mode, the netfs will fetch the data from
the remote server and then write it to the cache file; in on-demand
read mode, fetching the data and writing it into the cache is delegated
to a user daemon.

As the first step, notify the user daemon when looking up cookie. In
this case, an anonymous fd is sent to the user daemon, through which the
user daemon can write the fetched data to the cache file. Since the user
daemon may move the anonymous fd around, e.g. through dup(), an object
ID uniquely identifying the cache file is also attached.

Also add one advisory flag (FSCACHE_ADV_WANT_CACHE_SIZE) suggesting that
the cache file size shall be retrieved at runtime. This helps the
scenario where one cache file contains multiple netfs files, e.g. for
the purpose of deduplication. In this case, netfs itself has no idea the
size of the cache file, whilst the user daemon should give the hint on
it.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220509074028.74954-3-jefflexu@linux.alibaba.com
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
cachefiles: extract write routine 2022-05-17T16:11:17+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-04-25T12:21:23+00:00 a06fac1599c179853639491974fd72aefd46d030 Extract the generic routine of writing data to cache files, and make it generally available. This will be used by the following patch implementing on-demand read mode. Since it's called inside CacheFiles module, make the interface generic and unrelated to netfs_cache_resources. It is worth noting that, ki->inval_counter is not initialized after this cleanup. It shall not make any visible difference, since inval_counter is no longer used in the write completion routine, i.e. cachefiles_write_complete(). Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Acked-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/20220425122143.56815-2-jefflexu@linux.alibaba.com Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com> 
Extract the generic routine of writing data to cache files, and make it
generally available.

This will be used by the following patch implementing on-demand read
mode. Since it's called inside CacheFiles module, make the interface
generic and unrelated to netfs_cache_resources.

It is worth noting that, ki->inval_counter is not initialized after
this cleanup. It shall not make any visible difference, since
inval_counter is no longer used in the write completion routine, i.e.
cachefiles_write_complete().

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20220425122143.56815-2-jefflexu@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
cachefiles: Fix KASAN slab-out-of-bounds in cachefiles_set_volume_xattr 2022-04-08T22:32:40+00:00 Dave Wysochanski dwysocha@redhat.com 2022-04-05T13:46:49+00:00 7b2f6c306601240635c72caa61f682e74d4591b2 Use the actual length of volume coherency data when setting the xattr to avoid the following KASAN report. BUG: KASAN: slab-out-of-bounds in cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles] Write of size 4 at addr ffff888101e02af4 by task kworker/6:0/1347 CPU: 6 PID: 1347 Comm: kworker/6:0 Kdump: loaded Not tainted 5.18.0-rc1-nfs-fscache-netfs+ #13 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-4.fc34 04/01/2014 Workqueue: events fscache_create_volume_work [fscache] Call Trace: <TASK> dump_stack_lvl+0x45/0x5a print_report.cold+0x5e/0x5db ? __lock_text_start+0x8/0x8 ? cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles] kasan_report+0xab/0x120 ? cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles] kasan_check_range+0xf5/0x1d0 memcpy+0x39/0x60 cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles] cachefiles_acquire_volume+0x2be/0x500 [cachefiles] ? __cachefiles_free_volume+0x90/0x90 [cachefiles] fscache_create_volume_work+0x68/0x160 [fscache] process_one_work+0x3b7/0x6a0 worker_thread+0x2c4/0x650 ? process_one_work+0x6a0/0x6a0 kthread+0x16c/0x1a0 ? kthread_complete_and_exit+0x20/0x20 ret_from_fork+0x22/0x30 </TASK> Allocated by task 1347: kasan_save_stack+0x1e/0x40 __kasan_kmalloc+0x81/0xa0 cachefiles_set_volume_xattr+0x76/0x350 [cachefiles] cachefiles_acquire_volume+0x2be/0x500 [cachefiles] fscache_create_volume_work+0x68/0x160 [fscache] process_one_work+0x3b7/0x6a0 worker_thread+0x2c4/0x650 kthread+0x16c/0x1a0 ret_from_fork+0x22/0x30 The buggy address belongs to the object at ffff888101e02af0 which belongs to the cache kmalloc-8 of size 8 The buggy address is located 4 bytes inside of 8-byte region [ffff888101e02af0, ffff888101e02af8) The buggy address belongs to the physical page: page:00000000a2292d70 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x101e02 flags: 0x17ffffc0000200(slab|node=0|zone=2|lastcpupid=0x1fffff) raw: 0017ffffc0000200 0000000000000000 dead000000000001 ffff888100042280 raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff888101e02980: fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc fc fc ffff888101e02a00: 00 fc fc fc fc 00 fc fc fc fc 00 fc fc fc fc 00 >ffff888101e02a80: fc fc fc fc 00 fc fc fc fc 00 fc fc fc fc 04 fc ^ ffff888101e02b00: fc fc fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc ffff888101e02b80: fc fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc fc ================================================================== Fixes: 413a4a6b0b55 "cachefiles: Fix volume coherency attribute" Signed-off-by: Dave Wysochanski <dwysocha@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/20220405134649.6579-1-dwysocha@redhat.com/ # v1 Link: https://lore.kernel.org/r/20220405142810.8208-1-dwysocha@redhat.com/ # Incorrect v2 
Use the actual length of volume coherency data when setting the
xattr to avoid the following KASAN report.

 BUG: KASAN: slab-out-of-bounds in cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles]
 Write of size 4 at addr ffff888101e02af4 by task kworker/6:0/1347

 CPU: 6 PID: 1347 Comm: kworker/6:0 Kdump: loaded Not tainted 5.18.0-rc1-nfs-fscache-netfs+ #13
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-4.fc34 04/01/2014
 Workqueue: events fscache_create_volume_work [fscache]
 Call Trace:
  <TASK>
  dump_stack_lvl+0x45/0x5a
  print_report.cold+0x5e/0x5db
  ? __lock_text_start+0x8/0x8
  ? cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles]
  kasan_report+0xab/0x120
  ? cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles]
  kasan_check_range+0xf5/0x1d0
  memcpy+0x39/0x60
  cachefiles_set_volume_xattr+0xa0/0x350 [cachefiles]
  cachefiles_acquire_volume+0x2be/0x500 [cachefiles]
  ? __cachefiles_free_volume+0x90/0x90 [cachefiles]
  fscache_create_volume_work+0x68/0x160 [fscache]
  process_one_work+0x3b7/0x6a0
  worker_thread+0x2c4/0x650
  ? process_one_work+0x6a0/0x6a0
  kthread+0x16c/0x1a0
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x22/0x30
  </TASK>

 Allocated by task 1347:
  kasan_save_stack+0x1e/0x40
  __kasan_kmalloc+0x81/0xa0
  cachefiles_set_volume_xattr+0x76/0x350 [cachefiles]
  cachefiles_acquire_volume+0x2be/0x500 [cachefiles]
  fscache_create_volume_work+0x68/0x160 [fscache]
  process_one_work+0x3b7/0x6a0
  worker_thread+0x2c4/0x650
  kthread+0x16c/0x1a0
  ret_from_fork+0x22/0x30

 The buggy address belongs to the object at ffff888101e02af0
 which belongs to the cache kmalloc-8 of size 8
 The buggy address is located 4 bytes inside of
 8-byte region [ffff888101e02af0, ffff888101e02af8)

 The buggy address belongs to the physical page:
 page:00000000a2292d70 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x101e02
 flags: 0x17ffffc0000200(slab|node=0|zone=2|lastcpupid=0x1fffff)
 raw: 0017ffffc0000200 0000000000000000 dead000000000001 ffff888100042280
 raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
 ffff888101e02980: fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc fc fc
 ffff888101e02a00: 00 fc fc fc fc 00 fc fc fc fc 00 fc fc fc fc 00
 >ffff888101e02a80: fc fc fc fc 00 fc fc fc fc 00 fc fc fc fc 04 fc
                                                            ^
 ffff888101e02b00: fc fc fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc
 ffff888101e02b80: fc fc 00 fc fc fc fc 00 fc fc fc fc 00 fc fc fc
 ==================================================================

Fixes: 413a4a6b0b55 "cachefiles: Fix volume coherency attribute"
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/20220405134649.6579-1-dwysocha@redhat.com/ # v1
Link: https://lore.kernel.org/r/20220405142810.8208-1-dwysocha@redhat.com/ # Incorrect v2
cachefiles: unmark inode in use in error path 2022-04-08T22:32:30+00:00 Jeffle Xu jefflexu@linux.alibaba.com 2022-03-30T09:47:59+00:00 ea5dc046127e857a7873ae55fd57c866e9e86fb2 Unmark inode in use if error encountered. If the in-use flag leakage occurs in cachefiles_open_file(), Cachefiles will complain "Inode already in use" when later another cookie with the same index key is looked up. If the in-use flag leakage occurs in cachefiles_create_tmpfile(), though the "Inode already in use" warning won't be triggered, fix the leakage anyway. Reported-by: Gao Xiang <hsiangkao@linux.alibaba.com> Fixes: 1f08c925e7a3 ("cachefiles: Implement backing file wrangling") Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: linux-cachefs@redhat.com Link: https://listman.redhat.com/archives/linux-cachefs/2022-March/006615.html # v1 Link: https://listman.redhat.com/archives/linux-cachefs/2022-March/006618.html # v2 
Unmark inode in use if error encountered. If the in-use flag leakage
occurs in cachefiles_open_file(), Cachefiles will complain "Inode
already in use" when later another cookie with the same index key is
looked up.

If the in-use flag leakage occurs in cachefiles_create_tmpfile(), though
the "Inode already in use" warning won't be triggered, fix the leakage
anyway.

Reported-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Fixes: 1f08c925e7a3 ("cachefiles: Implement backing file wrangling")
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-cachefs@redhat.com
Link: https://listman.redhat.com/archives/linux-cachefs/2022-March/006615.html # v1
Link: https://listman.redhat.com/archives/linux-cachefs/2022-March/006618.html # v2