The following commit has been merged into the perf/urgent branch of tip:
Commit-ID: fa4f4bae893fbce8a3edfff1ab7ece0c01dc1328 Gitweb: https://git.kernel.org/tip/fa4f4bae893fbce8a3edfff1ab7ece0c01dc1328 Author: Adrian Hunter adrian.hunter@intel.com AuthorDate: Mon, 13 Oct 2025 10:22:44 +03:00 Committer: Peter Zijlstra peterz@infradead.org CommitterDate: Tue, 14 Oct 2025 10:38:10 +02:00
perf/core: Fix MMAP2 event device with backing files
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 --- kernel/events/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 7b5c237..177e57c 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9403,7 +9403,7 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event) flags |= MAP_HUGETLB;
if (file) { - struct inode *inode; + const struct inode *inode; dev_t dev;
buf = kmalloc(PATH_MAX, GFP_KERNEL); @@ -9421,7 +9421,7 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event) name = "//toolong"; goto cpy_name; } - inode = file_inode(vma->vm_file); + inode = file_user_inode(vma->vm_file); dev = inode->i_sb->s_dev; ino = inode->i_ino; gen = inode->i_generation;