From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.155 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793749596; b=saoh7Cg+G39s2HhCezrSDoKusl+N1I+EcjNgKzmdY8PGv9P18hLkQ7OmSHQ6kGsmeJKl RS6EBuxrBxL6zEd7TXuruMzlaKtLMqkEsUwE3HGrqlB9Zr0M0+3wtOtlcz/uflU31Ks7q Rwr/tXt4N4aVXIbi+7AFs4iJB+Qp/55g7e0pftZzU79t+bTD1qBP1WIp15Ux204fG0lOj 5QDCoHGs5jDaW9Ayb1/1bsZOHHkbQUuYHJMCNByql61fepbisJ1RfqGqcbJVoUNbmkyo2 Kz19d+oBdprePLCVWk+/pJDQqZm2kZ7eOyAyGr4nJe0nEzaigZZ9X/Q8Amv0bovxE/g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793749596; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=uPirOmTrSzR+qJbbu6ot8AJCfXQYDzCgUX4JayMeJqY=; b=FrtVsuOYsILQMBlA6McwdeI2ouoycxIZM46A4QCnc8wg4oKbvFMmHN8597dX8o4VJp7U DOlOb55esEVRtkP7HQpaiXGcPec6lPnxJJWKz1VAhh561/1c2c7ECFomiTTdYlJ7y7C3h ++zyPIYdnCH3pAuoEa8gpI5hEBPkLuwH/p4ieut22ggFXYj9rvSZy64sBD87OqhrjkXT+ PMlVG0O3rgwFH8N4yh7Gk6ZTKsPDqQtZVnafJdAfPr9HqoDWujZ3vjmIBelQfyi5nCzhg RiEOg4Xe1x+AseEsbvqtCpIYNYhS8Kl24d3XwLvJx1KbNpiTxW77P2qZJLCmThMqmfw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=KpKAPSYG; arc=none smtp.remote-ip=91.218.175.155 Received: from mta0.migadu.com (out-155.mta0.migadu.com [91.218.175.155]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6B8B9606D83E for ; Tue, 3 Nov 2026 23:46:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 6B8B9606D83E Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=KpKAPSYG X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=1mASqXNaXoMjNQ3SMMIKGa4jpTD7lgU+gHYsGfukTD4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793749592; v=1; x=1794354392; b=KpKAPSYGEs9xzCE/nniJ+D+PcFDzoE48xaJeKxYfna/UkNhwiNx6iPbsfUjBnSZo/KSk4gWZ MXzJ0L9NeSEuA80HOG9jmGCXPRSBuyMsKn7W22a/6aB2cG9U0B/iqK9LHyKrgdFA0fyIwbzVj47 yZq0Pma41EhlOOBJnBYTiYTo= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 353126e08cf0d14c; Tue, 03 Nov 2026 23:46:31 +0000 X-Mizu-Trace-ID: 353126e08cf0d14c X-Migadu-Flow: FLOW_OUT Message-ID: Date: Tue, 3 Nov 2026 15:46:27 -0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC bpf-next 0/2] bpf: Do not let preemption cause false recursion drops in trampoline progs To: Alexei Starovoitov , mikeba@sentinelone.com, Daniel Borkmann , Andrii Nakryiko Cc: Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , John Fastabend , Shuah Khan , bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261025-b4-bpf-trampoline-preempt-v1-0-198dcdc0c6ac@sentinelone.com> Content-Language: en-US From: JP Kobryn In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/30/26 3:22 PM, Alexei Starovoitov wrote: > On Sun, Oct 25, 2026 at 04:02 AM Mike Bazov via B4 Relay wrote: > >> Is disabling preemption in __bpf_prog_enter_recur() on !PREEMPT_RT the >> preferred fix for fentry/fexit, or would you prefer a different >> mechanism for reconciling preemptible execution with prog->active and >> the per-CPU private stack? > > No. > We cannot disable preemption, since progs are not short > with may_goto they can take 1/4 sec. Seeing this issue as well. This patch opts in ALL non-sleepable programs with trampolines. Alexei, would your thoughts be the same if there was an opt-in approach, like a libbpf annotation "fentry.nonpreempt", for select programs? A patch like this could then check if program->nonpreempt is set.