From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 8BA08239082 for ; Wed, 2 Apr 2025 12:16:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743596190; cv=none; b=g4FkKZndn7gsAAA5U17XdbnryXipPRpEHSw+dMtGMcnCrSIMGjHLpeyw+HQUTidcevs6/xJpYAG3DaVEWSPS1/zARwjIjz1oiYWSPZ3irWipbcdchFdzEE0uGSB2TaWv0L4AsI9VpdK0h3fcUdrdtKRt8lPj4cPDqna2AM7cGIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743596190; c=relaxed/simple; bh=59947Uzvz/Wz9HkcMH9W6ivrjIBdj/ddLa4eFtJ6O48=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CkNd/7fF8svOZbT5/a8Cgq8krE6vUXmf7FP3lV1aNlrIFPwdC+oK5GvFNdoJNN8emH8bwUMYw2bwihqSEYsDXdjlT+dSrNrNBGiN+oY3F654e4pXxtQqCqxg/o+GzAXZkdEKi0fo4YXZTLdj9zidmtFKqhXWB8Gjzuy1nc6d6/s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=tH6g8IAf; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=CbT04qDU; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="tH6g8IAf"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="CbT04qDU" Date: Wed, 2 Apr 2025 14:16:24 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1743596186; 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=hQk4WQsPf11N7Iy+mIpH3whaONZtx1TFQpD1Yg1zXaQ=; b=tH6g8IAf+WIhTI3cb6YfvB3LAjnqpV55NX+GAqjr+NSlKJAvyalL1AYQUcgY2zyeCLRWAm 421gpGh3HnLmzhSif34ze/Mp263yc/bMzD7bPPKcC7Nb5RdutPC4iVOnE6T9fYcsuGQqd1 hNZMluNgLRlTKElKLuOP0nhBHT8LVvogkFhPDmovUN0GjKoPkx9EkgnNg818ITIzb1UiuJ lT9OmTme22vHqbxacEIu6TBSo3WaupZ2A5TyKcHnd4ooWzyJVPy543EDit6po9xR3XaIqP wniL4q+2eyprvAwfdF+0wk3y4cCQivoHxcCCyTLV4WcX0og6Cpa60jhFWTajBA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1743596186; 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=hQk4WQsPf11N7Iy+mIpH3whaONZtx1TFQpD1Yg1zXaQ=; b=CbT04qDUJsDGlgyLyNz33oIxANPd6wcVARTAoIYW4V86ySWdSUUCAG9OlpXFTJdi5zdQvS S99+C8yIN4a3sjCg== From: Sebastian Sewior To: Oleg Nesterov Cc: Alexei Starovoitov , Peter Ziljstra , Andrii Nakryiko , bpf , Steven Rostedt , Jiri Olsa , Masami Hiramatsu Subject: Re: uprobe splat in PREEMP_RT Message-ID: <20250402121624.lRIPMa_h@linutronix.de> References: <20250402091044.GB22091@redhat.com> <20250402105444.tW8UU7vO@linutronix.de> <20250402112007.GE22091@redhat.com> <20250402113142.GG22091@redhat.com> <20250402120649._gQHEtYM@linutronix.de> <20250402121228.GH22091@redhat.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250402121228.GH22091@redhat.com> On 2025-04-02 14:12:28 [+0200], Oleg Nesterov wrote: > On 04/02, Sebastian Sewior wrote: > > > > On 2025-04-02 13:31:43 [+0200], Oleg Nesterov wrote: > > > > > > IOW. > > > > > > I understand that seqcount_t is not RT-friendly, but why exactly do > > > you think the patch above can make the things worse? > > > > We wouldn't notice such a case. > > Sebastian, could you spell please? > > What case we wouldn't notice? I'm sorry. It wouldn't notice that preemption isn't disabled and yell. > With this patch write_seqcount_begin(seqcount_t) will notice that > seqprop_preemptible() is true and do preempt_disable() itself. Yes, but that we don't want. This would disable preemption for the whole section and not allow anything on PREEMPT_RT what would be possible otherwise. Like acquire a spinlock_t or so. Yes, none of this would affect hprobe_expire(). > Oleg. Sebastian