linux-kernel - Re: [PATCH 7/8] uprobes: perform lockless SRCU-protected uprobes

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Message-ID: <20240810140015.GA21800@redhat.com>
Date: Sat, 10 Aug 2024 16:00:15 +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
Subject: Re: [PATCH 7/8] uprobes: perform lockless SRCU-protected
 uprobes_tree lookup

On 08/08, Oleg Nesterov wrote:
>
> On 07/31, Andrii Nakryiko wrote:
> >
> >  static DEFINE_RWLOCK(uprobes_treelock);	/* serialize rbtree access */
> > +static seqcount_rwlock_t uprobes_seqcount = SEQCNT_RWLOCK_ZERO(uprobes_seqcount, &uprobes_treelock);
>
> Just noticed... Why seqcount_rwlock_t?
>
> find_uprobe_rcu() doesn't use read_seqbegin_or_lock(),
> seqcount_t should work just fine.

Please ignore... I forgot that seqcount_t is not CONFIG_PREEMPT_RT-friendly.

Hmm. __seqprop_preemptible() returns 0, this doesn't look right... Nevermend.

Oleg.