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fa4f4bae89
Some file systems like FUSE-based ones or overlayfs may record the backing
file in struct vm_area_struct vm_file, instead of the user file that the
user mmapped.
That causes perf to misreport the device major/minor numbers of the file
system of the file, and the generation of the file, and potentially other
inode details. There is an existing helper file_user_inode() for that
situation.
Use file_user_inode() instead of file_inode() to get the inode for MMAP2
events.
Example:
Setup:
# cd /root
# mkdir test ; cd test ; mkdir lower upper work merged
# cp `which cat` lower
# mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merged
# perf record -e cycles:u -- /root/test/merged/cat /proc/self/maps
...
55b2c91d0000-55b2c926b000 r-xp 00018000 00:1a 3419 /root/test/merged/cat
...
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.004 MB perf.data (5 samples) ]
#
# stat /root/test/merged/cat
File: /root/test/merged/cat
Size: 1127792 Blocks: 2208 IO Block: 4096 regular file
Device: 0,26 Inode: 3419 Links: 1
Access: (0755/-rwxr-xr-x) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2025-09-08 12:23:59.453309624 +0000
Modify: 2025-09-08 12:23:59.454309624 +0000
Change: 2025-09-08 12:23:59.454309624 +0000
Birth: 2025-09-08 12:23:59.453309624 +0000
Before:
Device reported 00:02 differs from stat output and /proc/self/maps
# perf script --show-mmap-events | grep /root/test/merged/cat
cat 377 [-01] 243.078558: PERF_RECORD_MMAP2 377/377: [0x55b2c91d0000(0x9b000) @ 0x18000 00:02 3419 2068525940]: r-xp /root/test/merged/cat
After:
Device reported 00:1a is the same as stat output and /proc/self/maps
# perf script --show-mmap-events | grep /root/test/merged/cat
cat 362 [-01] 127.755167: PERF_RECORD_MMAP2 362/362: [0x55ba6e781000(0x9b000) @ 0x18000 00:1a 3419 0]: r-xp /root/test/merged/cat
With respect to stable kernels, overlayfs mmap function ovl_mmap() was
added in v4.19 but file_user_inode() was not added until v6.8 and never
back-ported to stable kernels. FMODE_BACKING that it depends on was added
in v6.5. This issue has gone largely unnoticed, so back-porting before
v6.8 is probably not worth it, so put 6.8 as the stable kernel prerequisite
version, although in practice the next long term kernel is 6.12.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Amir Goldstein <amir73il@gmail.com>
Cc: stable@vger.kernel.org # 6.8
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.