Build id fix.v6.draft#12153
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Factor out helpers from stack_map_get_build_id_offset() in preparation for adding a sleepable build ID resolution path. No functional changes. Acked-by: Mykyta Yatsenko <yatsenko@meta.com> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Sleepable build ID parsing can block in __kernel_read(), so the stackmap sleepable path must not call it while holding mmap_lock or a per-VMA read lock. The issue and the fix are conceptually similar to a recent procfs patch. Resolve each covered VMA with a stable read-side reference, preferring lock_vma_under_rcu() and falling back to mmap_read_trylock() only long enough to acquire the VMA read lock. Take a reference to the backing file, snapshot the file offset, drop the VMA lock, and then parse the build ID through (sleepable) build_id_parse_file(). We have to use mmap_read_trylock() (and give up on failure) in this context because taking mmap_read_lock() is generally unsafe on code paths reachable from BPF programs, and may lead to deadlocks. [1] https://lore.kernel.org/all/20251218005818.614819-1-shakeel.butt@linux.dev/ [2] https://lore.kernel.org/all/20260128183232.2854138-1-andrii@kernel.org/ [3] https://lore.kernel.org/bpf/2895ecd8-df1e-4cc0-b9f9-aef893dc2360@linux.dev/ Fixes: d4dd977 ("bpf: wire up sleepable bpf_get_stack() and bpf_get_task_stack() helpers") Suggested-by: Puranjay Mohan <puranjay@kernel.org> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Stack traces often contain adjacent IPs from the same VMA or from different VMAs backed by the same ELF file. Cache the last successfully parsed build id together with the resolved VMA range and backing file so the sleepable build id path can avoid repeated VMA locking and file parsing in common cases. Use the shared build id result helper for cache hits and the slow path so the cache logic can return directly from each resolved case without a common goto target. Suggested-by: Mykyta Yatsenko <yatsenko@meta.com> Acked-by: Mykyta Yatsenko <yatsenko@meta.com> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
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