linux-kernel - Re: [PATCH v4 tip/perf/core 0/4] uprobes,mm: speculative lockless VMA-to-uprobe lookup

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Message-ID: <CAEf4BzYPajbgyvcvm7z1EiPgkee1D1r=a8gaqxzd7k13gh9Uzw@mail.gmail.com>
Date: Tue, 5 Nov 2024 18:01:25 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Andrii Nakryiko <andrii@...nel.org>
Cc: linux-trace-kernel@...r.kernel.org, linux-mm@...ck.org, 
	akpm@...ux-foundation.org, peterz@...radead.org, oleg@...hat.com, 
	rostedt@...dmis.org, mhiramat@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, jolsa@...nel.org, paulmck@...nel.org, 
	willy@...radead.org, surenb@...gle.com, mjguzik@...il.com, brauner@...nel.org, 
	jannh@...gle.com, mhocko@...nel.org, vbabka@...e.cz, shakeel.butt@...ux.dev, 
	hannes@...xchg.org, Liam.Howlett@...cle.com, lorenzo.stoakes@...cle.com, 
	david@...hat.com, arnd@...db.de, richard.weiyang@...il.com, 
	zhangpeng.00@...edance.com, linmiaohe@...wei.com, viro@...iv.linux.org.uk, 
	hca@...ux.ibm.com
Subject: Re: [PATCH v4 tip/perf/core 0/4] uprobes,mm: speculative lockless
 VMA-to-uprobe lookup

On Sun, Oct 27, 2024 at 6:09 PM Andrii Nakryiko <andrii@...nel.org> wrote:
>
> Implement speculative (lockless) resolution of VMA to inode to uprobe,
> bypassing the need to take mmap_lock for reads, if possible. First two patches
> 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 #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
>
> v3->v4:
> - rebased and dropped data_race(), given mm_struct uses real seqcount (Peter);
> 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 (2):
>   uprobes: simplify find_active_uprobe_rcu() VMA checks
>   uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution
>
> Suren Baghdasaryan (2):
>   mm: Convert mm_lock_seq to a proper seqcount
>   mm: Introduce mmap_lock_speculation_{begin|end}
>
>  include/linux/mm.h               | 12 ++---
>  include/linux/mm_types.h         |  7 ++-
>  include/linux/mmap_lock.h        | 87 ++++++++++++++++++++++++--------
>  kernel/events/uprobes.c          | 47 ++++++++++++++++-
>  kernel/fork.c                    |  5 +-
>  mm/init-mm.c                     |  2 +-
>  tools/testing/vma/vma.c          |  4 +-
>  tools/testing/vma/vma_internal.h |  4 +-
>  8 files changed, 129 insertions(+), 39 deletions(-)
>
> --
> 2.43.5
>

Hi!

What's the status of this patch set? Are there any blockers for it to
be applied to perf/core? MM folks are OK with landing the first two
patches in perf/core, so hopefully we should be good to go?