Re: [PATCH bpf v4 2/3] bpf: Avoid faultable build ID reads under mm locks

[Shakeel Butt]

On Thu, May 14, 2026 at 11:47:26AM -0700, Ihor Solodrai wrote:
> Sleepable build ID parsing can block in __kernel_read() [1], 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 [2].
> 
> Resolve each covered VMA with a stable read-side reference, preferring
> lock_vma_under_rcu() and falling back to mmap_read_trylock()

Why trylock()? Why not just reuse the mechanism introduced in [2]? That is
abstract out the mechanism introduced in [2] in mm core and reuse it.


> only long
> enough to acquire the VMA read lock. Take a reference to the backing
> file, drop the VMA lock, and then parse the build ID through
> (sleepable) build_id_parse_file().
> 
> [1]: https://lore.kernel.org/all/20251218005818.614819-1-shakeel.butt@xxxxxxxxx/
> [2]: https://lore.kernel.org/all/20260128183232.2854138-1-andrii@xxxxxxxxxx/
>