linux-kernel - Re: [PATCH v2 tip/perf/core 0/5] uprobes,mm: speculative lockless VMA-to-uprobe lookup

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Message-ID: <20241008152056.GA9508@redhat.com>
Date: Tue, 8 Oct 2024 17:20:57 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andrii Nakryiko <andrii@...nel.org>
Cc: linux-trace-kernel@...r.kernel.org, peterz@...radead.org,
	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, akpm@...ux-foundation.org,
	linux-mm@...ck.org, mjguzik@...il.com, brauner@...nel.org,
	jannh@...gle.com, mhocko@...nel.org, vbabka@...e.cz,
	mingo@...nel.org
Subject: Re: [PATCH v2 tip/perf/core 0/5] uprobes,mm: speculative lockless
 VMA-to-uprobe lookup

Well. I am in no position to ack these changes.

But let me say that I personally like this series and I see nothing wrong,
except perhaps 5/5 needs some data_race/etc annotations as we have already
discussed.

Thanks,

Oleg.

On 10/01, Andrii Nakryiko 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 were 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).
>
> Patch #3 adds back RCU-delayed freeing for FMODE_BACKING files, which is
> necessary to make speculation safe to access struct file's memory in any
> possible situation.
>
> Patch #4 is a simplification to uprobe VMA flag checking, suggested by Oleg.
>
> And, finally, patch #5 is the speculative VMA-to-uprobe resolution logic. See
> corresponding patch for details and benchmarking results.
>
> 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 (4):
>   mm: switch to 64-bit mm_lock_seq/vm_lock_seq on 64-bit architectures
>   fs: add back RCU-delayed freeing of FMODE_BACKING file
>   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}
>
>  fs/file_table.c           |  2 +-
>  include/linux/mm.h        |  6 ++--
>  include/linux/mm_types.h  |  7 ++--
>  include/linux/mmap_lock.h | 72 ++++++++++++++++++++++++++++++++-------
>  kernel/events/uprobes.c   | 46 ++++++++++++++++++++++++-
>  kernel/fork.c             |  3 --
>  6 files changed, 114 insertions(+), 22 deletions(-)
>
> --
> 2.43.5
>