Re: [PATCH v3 tip/perf/core 0/4] uprobes,mm: speculative lockless VMA-to-uprobe lookup

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Oct 10, 2024 at 1:56 PM Andrii Nakryiko <andrii@kernel.org> wrote:
>
> Implement speculative (lockless) resolution of VMA to inode to uprobe,
> bypassing the need to take mmap_lock for reads, if possible. Patch #1 by Suren
> adds mm_struct helpers that help detect whether mm_struct was changed, which
> is used by uprobe logic to validate that speculative results can be trusted
> after all the lookup logic results in a valid uprobe instance. Patch #2
> follows to make mm_lock_seq into 64-bit counter (on 64-bit architectures), as
> requested by Jann Horn.
>
> Patch #3 is a simplification to uprobe VMA flag checking, suggested by Oleg.
>
> And, finally, patch #4 is the speculative VMA-to-uprobe resolution logic
> itself, and is the focal point of this patch set. It makes entry uprobes in
> common case scale very well with number of CPUs, as we avoid any locking or
> cache line bouncing between CPUs. See corresponding patch for details and
> benchmarking results.
>
> Note, this patch set assumes that FMODE_BACKING files were switched to have
> SLAB_TYPE_SAFE_BY_RCU semantics, which was recently done by Christian Brauner
> in [0]. This change can be pulled into perf/core through stable
> tags/vfs-6.13.for-bpf.file tag from [1].
>
>   [0] https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?h=vfs-6.13.for-bpf.file&id=8b1bc2590af61129b82a189e9dc7c2804c34400e
>   [1] git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
>
> v2->v3:
> - dropped kfree_rcu() patch (Christian);
> - added data_race() annotations for fields of vma and vma->vm_file which could
>   be modified during speculative lookup (Oleg);
> - fixed int->long problem in stubs for mmap_lock_speculation_{start,end}(),
>   caught by Kernel test robot;
> v1->v2:
> - adjusted vma_end_write_all() comment to point out it should never be called
>   manually now, but I wasn't sure how ACQUIRE/RELEASE comments should be
>   reworded (previously requested by Jann), so I'd appreciate some help there
>   (Jann);
> - int -> long change for mm_lock_seq, as agreed at LPC2024 (Jann, Suren, Liam);
> - kfree_rcu_mightsleep() for FMODE_BACKING (Suren, Christian);
> - vm_flags simplification in find_active_uprobe_rcu() and
>   find_active_uprobe_speculative() (Oleg);
> - guard(rcu)() simplified find_active_uprobe_speculative() implementation.
>
> Andrii Nakryiko (3):
>   mm: switch to 64-bit mm_lock_seq/vm_lock_seq on 64-bit architectures
>   uprobes: simplify find_active_uprobe_rcu() VMA checks
>   uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution
>
> Suren Baghdasaryan (1):
>   mm: introduce mmap_lock_speculation_{start|end}
>
>  include/linux/mm.h        |  6 ++--
>  include/linux/mm_types.h  |  7 ++--
>  include/linux/mmap_lock.h | 72 ++++++++++++++++++++++++++++++++-------
>  kernel/events/uprobes.c   | 52 +++++++++++++++++++++++++++-
>  kernel/fork.c             |  3 --
>  5 files changed, 119 insertions(+), 21 deletions(-)
>
> --
> 2.43.5
>

This applies cleanly to tip/perf/core with or without Jiri's patches
([0]). No need to rebase and resend, this is ready to go in.

  [0] https://lore.kernel.org/all/20241018202252.693462-1-jolsa@kernel.org/