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e30453c61e
shrinker_debugfs_add() creates both "count" and "scan" debugfs files
unconditionally.
That assumes every shrinker implements both count_objects() and
scan_objects(), which is not guaranteed. For example, the xen-backend
shrinker sets count_objects() but leaves scan_objects() NULL, so writing
to its scan file calls through a NULL function pointer and panics the
kernel:
BUG: kernel NULL pointer dereference, address: 0000000000000000
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
Call Trace:
<TASK>
shrinker_debugfs_scan_write+0x12e/0x270
full_proxy_write+0x5f/0x90
vfs_write+0xde/0x420
? filp_flush+0x75/0x90
? filp_close+0x1d/0x30
? do_dup2+0xb8/0x120
ksys_write+0x68/0xf0
? filp_flush+0x75/0x90
do_syscall_64+0xb3/0x5b0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
The count path has the same issue in principle if a shrinker omits
count_objects().
To fix it, only create "count" and "scan" debugfs files when the
corresponding callbacks are present.
Link: https://lore.kernel.org/20260617090052.27325-1-qi.zheng@linux.dev
Fixes: bbf535fd6f ("mm: shrinkers: add scan interface for shrinker debugfs")
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
270 lines
5.9 KiB
270 lines
5.9 KiB