From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2FA561C57A7 for ; Wed, 7 Aug 2024 10:18:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723025882; cv=none; b=Pw1k4SBStGeaaIArbcjULoIKg7p9N0f8Gvfq242HYlVwR4rBaJ1XrLvYNkx2Hwrxqcct8IPU9vl4YwT0MGlIRVVqHz4ZFO/Nb4QlLayy5cp1omwP78ruhTIb+Wc7n4e3uCt4i/pIj818o0P95Mr+izLibVin2Mwz5evAVzisn2c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723025882; c=relaxed/simple; bh=dU34Jk/zdBG66KdZqoSvUYqEsvh2JWx8pa6AroZH7QU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SKa0c/AW2G8hD+hMv3Ltj/6BFiAZ1+uOsdbMc8FhNvFmS8Fpe509ltd8J+7Jmx07lUbdZJUpZpiEEuOs3UeMwcuUF7yjts6pAeQ9+GMe2j5oLwKBFQAHEb7GxlaAxy9rysi5aCyFIksyGTFYtxcooI6ZzxQeCRm7/8Gn4kl16wE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=Md03+38X; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Md03+38X" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1723025880; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=fToBX/B6bWnrDNLZMpsbxGATEy0ptfzvMuaWk2wqyMQ=; b=Md03+38XY5Ro8K9x3fek8GWV0dCNsemcZI9HMg+n3Ez+ZGwc4yFsg2MQhiqrggoYQrmTe7 0Ulbs39jmOLsN+cGVV/S7VeqaJmyAwdNeIvA2OgEMCaEprenZ1VJaUU8thCEldRj9g2mFC XC1v9mErSkbBpovW+GUj+wlX5qO3Q2g= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-303-nAzyQwZnOiWBYSemnvehCg-1; Wed, 07 Aug 2024 06:17:58 -0400 X-MC-Unique: nAzyQwZnOiWBYSemnvehCg-1 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 419A01944AA9; Wed, 7 Aug 2024 10:17:55 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.97]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 118BD1953BB9; Wed, 7 Aug 2024 10:17:49 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 7 Aug 2024 12:17:53 +0200 (CEST) Date: Wed, 7 Aug 2024 12:17:47 +0200 From: Oleg Nesterov To: "Liao, Chang" Cc: mhiramat@kernel.org, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Subject: Re: [PATCH] uprobes: Improve scalability by reducing the contention on siglock Message-ID: <20240807101746.GA27715@redhat.com> References: <20240801082407.1618451-1-liaochang1@huawei.com> <20240801140639.GE4038@redhat.com> <51a756b7-3c2f-9aeb-1418-b38b74108ee6@huawei.com> <20240802092406.GC12343@redhat.com> <0c69ef28-26d8-4b6e-fa78-2211a7b84eca@huawei.com> <20240806172529.GC20881@redhat.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240806172529.GC20881@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 So. Liao, I am sorry, but I dislike your patch/approach in any case. UTASK_SSTEP_DENY_SIGNAL complicates the state machine. And I don't like the fact that set_thread_flag(TIF_SIGPENDING) is called twice, from handle_singlestep() and uprobe_post_sstep_notifier(), this complicates the logic even more. We need a flag, not the new state. And if I read this patch correctly it is wrong: - uprobe_deny_signal() clears TIF_SIGPENDING and sets UTASK_SSTEP_DENY_SIGNAL - another signal cames after that and sets TIF_SIGPENDING again - in this case the task won't return to user-space and execute the probed insn, exit_to_user_mode_loop() will notice another TIF_SIGPENDING and call arch_do_signal_or_restart()->get_signal() again. - get_signal() will call uprobe_deny_signal() again hit WARN_ON_ONCE(utask->state != UTASK_SSTEP); And no, we shouldn't change this check into UTASK_SSTEP || UTASK_SSTEP_DENY_SIGNAL. Again, the fact that uprobe_deny_signal() cleared TIF_SIGPENDING must not be the new state. Oleg. On 08/06, Oleg Nesterov wrote: > > On 08/06, Liao, Chang wrote: > > > > You're absolutely right. handle_signlestep() has chance to handle _DENY_SIGANL > > unless it followed by setting TIF_UPROBE in uprobe_deny_signal(). This means > > _DENY_SIGNAL is likey replaced during next uprobe single-stepping. > > > > I believe introducing _DENY_SIGNAL as the immediate state between UTASK_SSTEP > > and UTASK_SSTEP_ACK is still necessary. This allow uprobe_post_sstep_notifier() > > to correctly restore TIF_SIGPENDING upon the completion of single-step. > > > > A revised implementation would look like this: > > Still looks "obviously wrong" to me... even the approach itself. > > Perhaps I am wrong, yet another day when I can't even read emails on lkml > carefully, sorry. > > But can you please send the patch which I could actually apply? This one > looks white-space damaged... > > I'll try to reply with more details as soon I convince myself I fully > understand what does your patch actually do, but most probably not tomorrow. > > Thanks, > > Oleg. > > > ------------------%<------------------ > > --- a/kernel/events/uprobes.c > > +++ b/kernel/events/uprobes.c > > @@ -1980,6 +1980,7 @@ bool uprobe_deny_signal(void) > > > > if (task_sigpending(t)) { > > clear_tsk_thread_flag(t, TIF_SIGPENDING); > > + utask->state = UTASK_SSTEP_DENY_SIGNAL; > > > > if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) { > > utask->state = UTASK_SSTEP_TRAPPED; > > @@ -2276,22 +2277,23 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs) > > int err = 0; > > > > uprobe = utask->active_uprobe; > > - if (utask->state == UTASK_SSTEP_ACK) > > + switch (utask->state) { > > + case UTASK_SSTEP_ACK: > > err = arch_uprobe_post_xol(&uprobe->arch, regs); > > - else if (utask->state == UTASK_SSTEP_TRAPPED) > > + break; > > + case UTASK_SSTEP_TRAPPED: > > arch_uprobe_abort_xol(&uprobe->arch, regs); > > - else > > + set_thread_flag(TIF_SIGPENDING); > > + break; > > + default: > > WARN_ON_ONCE(1); > > + } > > > > put_uprobe(uprobe); > > utask->active_uprobe = NULL; > > utask->state = UTASK_RUNNING; > > xol_free_insn_slot(current); > > > > - spin_lock_irq(¤t->sighand->siglock); > > - recalc_sigpending(); /* see uprobe_deny_signal() */ > > - spin_unlock_irq(¤t->sighand->siglock); > > - > > if (unlikely(err)) { > > uprobe_warn(current, "execute the probed insn, sending SIGILL."); > > force_sig(SIGILL); > > @@ -2351,6 +2353,8 @@ int uprobe_post_sstep_notifier(struct pt_regs *regs) > > /* task is currently not uprobed */ > > return 0; > > > > + if (utask->state == UTASK_SSTEP_DENY_SIGNAL) > > + set_thread_flag(TIF_SIGPENDING); > > utask->state = UTASK_SSTEP_ACK; > > set_thread_flag(TIF_UPROBE); > > return 1; > > > > ------------------>%------------------ > > > > > > > > Oleg. > > > > > > > > > > -- > > BR > > Liao, Chang > >