From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 3E3D32FCC12 for ; Mon, 10 Nov 2025 09:27:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762766854; cv=none; b=aCUsO1Qxo6x4+ZCQAL+spwULWSexRqHLZogoaBLWCan2g84eDhapmonSXSjQBMBLI7EUOEku7eoNGcJBroIHshEkvg14ucOn7bbr3pZzSSeg4SYX1wATB2e9Dt4ZF7gPoC7uDl4urFTd38iiPpZmlQHN4lfi9bAXzd26OoCrn6I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762766854; c=relaxed/simple; bh=0y1x6vuTqY1a4bcKRJr6zJO92StO1GY4H2TcgO+Dxqc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=M0Oa6jXScL6ADjLIMRPmoImc58HBsonRz/j/d93pe1sXLnHYcD/dmowIAsUiEtDIUWNB+rpYq2+BNTxAcJmfSNLvNV7bvjOJhDFfWcsWBB1ubzVYHHVWmuDPpa2qLz+aPZhWWkwp8a5IrrREAsnAaRX68cG0hC4JM1rl01REyms= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=jqbUXIZB; arc=none smtp.client-ip=95.215.58.174 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) header.d=linux.dev header.i=@linux.dev header.b="jqbUXIZB" Message-ID: <3d26b162-d218-41ec-b5ab-3657eaffadf6@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1762766839; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=45w11IYUjkqWJv5rhQ2qNwbknmdZ/cYVdBVIbaYQLFQ=; b=jqbUXIZBGWeJW5cmG+92WJ8dqj1WnvF2UMEmTKPmyy9OR0qwI2HnIxlJoJ6pLhgHZFPSt+ oxAI4CVUjt05ctOjeDqz1kJbcPlRq4IjY8xQG9yj7VZ/fl4fk+E3CtCI98048kWYEuNiWv 9BjBMMN9l63HZs6F8oxK3TSoTpGJBBc= Date: Mon, 10 Nov 2025 17:26:42 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v5 2/3] perf: Add atomic operation in get_recursion_context To: Peter Zijlstra Cc: 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-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Yonghong Song References: <20251109163559.4102849-1-chen.dylane@linux.dev> <20251109163559.4102849-3-chen.dylane@linux.dev> <20251110085210.GV3245006@noisy.programming.kicks-ass.net> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Tao Chen In-Reply-To: <20251110085210.GV3245006@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2025/11/10 16:52, Peter Zijlstra 写道: > On Mon, Nov 10, 2025 at 12:35:58AM +0800, Tao Chen wrote: >> From BPF side, preemption usually is enabled. Yonghong said, it is >> possible that both tasks (at process level) may reach right before >> "recursion[rctx]++;". In such cases, both tasks will be able to get >> buffer and this is not right. >> >> Signed-off-by: Yonghong Song >> Signed-off-by: Tao Chen >> --- > > Nope, this function really is meant to be used with preemption disabled. > If BPF doesn't abide, fix that. > Ok, let us use preempt_disable in bpf stackmap, thanks. I will change it in v6. >> kernel/events/internal.h | 5 +---- >> 1 file changed, 1 insertion(+), 4 deletions(-) >> >> diff --git a/kernel/events/internal.h b/kernel/events/internal.h >> index d9cc5708309..684bde972ba 100644 >> --- a/kernel/events/internal.h >> +++ b/kernel/events/internal.h >> @@ -214,12 +214,9 @@ static inline int get_recursion_context(u8 *recursion) >> { >> unsigned char rctx = interrupt_context_level(); >> >> - if (recursion[rctx]) >> + if (cmpxchg(&recursion[rctx], 0, 1) != 0) >> return -1; >> >> - recursion[rctx]++; >> - barrier(); >> - >> return rctx; >> } >> >> -- >> 2.48.1 >> -- Best Regards Tao Chen