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eedc8474d4
hugetlb_cgroup_css_alloc() rounds the counter limit down to a multiple of
the huge page size and then applies it inside an assertion:
VM_BUG_ON(page_counter_set_max(fault, limit));
VM_BUG_ON(page_counter_set_max(rsvd, limit));
With CONFIG_DEBUG_VM=n, VM_BUG_ON(cond) is BUILD_BUG_ON_INVALID(cond),
i.e. ((void)(sizeof((__force long)(cond)))), whose operand is never
evaluated. page_counter_set_max() is not a predicate - it performs
xchg(&counter->max, nr_pages) - so on every non-debug kernel the limit is
never applied and the counters keep page_counter_init()'s
PAGE_COUNTER_MAX.
That is user-visible, because hugetlb_cgroup_read_u64_max() recomputes the
same rounded value and uses equality as its "unlimited" sentinel.
PAGE_COUNTER_MAX is LONG_MAX / PAGE_SIZE = 2251799813685247, which is odd,
so round_down() really does change it and the two sides disagree. With
CONFIG_DEBUG_VM=n:
$ cat /sys/fs/cgroup/t/hugetlb.2MB.max
9223372036854771712
and with this patch:
$ cat /sys/fs/cgroup/t/hugetlb.2MB.max
max
A debug option should not change cgroup output.
Call the function, then assert the result, as v6.12 did. Use
VM_WARN_ON_ONCE() rather than restoring VM_BUG_ON(): the two are identical
under CONFIG_DEBUG_VM=n, and checkpatch asks that new code not use BUG()
variants.
Link: https://lore.kernel.org/20260817103433.191266-1-njilav@gmail.com
Fixes:
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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