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dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=goodmis.org header.i=@goodmis.org header.a=rsa-sha256 header.s=dkim1 header.b=zUOHQ6XH Received: from omf14.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id A2E79C0180; Fri, 23 Oct 2026 17:09:48 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf14.hostedemail.com (Postfix) with ESMTPA id 45F2E30; Fri, 23 Oct 2026 17:09:46 +0000 (UTC) Date: Fri, 23 Oct 2026 13:09:43 -0400 From: Steven Rostedt To: Jerome Marchand Cc: Michael Ellerman , Nicholas Piggin , Christophe Leroy , Ritesh Harjani , Shrikanth Hegde , Madhavan Srinivasan , Masami Hiramatsu , Mathieu Desnoyers , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] powerpc: Use raw_local_irq_pmu_save/restore() in local_t functions Message-ID: <20261023130943.775b2b65@gandalf.local.home> In-Reply-To: <20261023155529.3895393-1-jmarchan@redhat.com> References: <20261023155529.3895393-1-jmarchan@redhat.com> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspamout06 X-Stat-Signature: dkd49bp7ie9q1ukpuri763w5nzcejt5a X-Rspamd-Queue-Id: 45F2E30 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/0wX9pO02ZWtXsM9Kya2cXD7k+9fbyk8Q= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=8m4RKkMiiU8bh0E91081ZTnsfbzeWqjKyYPrm7qreTc=; b=zUOHQ6XHb8k5FmnnTjDdDC3cfTDXs9E6/Ow/oHOFpxNl40ZCyaAIvD9/OHZjWt99Kx13XgneXmdpyWmrYgdTjUHs7WZtaQkuCTpNi/RVnOwc4FsxqNcY8MsBG2NsCzVkzTY2n3KlyjMw9M4K0i+K5cqtZ6s1TbOyNfqfCuAA7NM= X-HE-Tag: 1792775386-597871 X-HE-Meta: U2FsdGVkX1+KkNW6m+t9S1AvyAQdJ3NdBfSGduko+1ErfnQswKcHgIVurgl/PvL/JYZgmf8Laz9ai/H6APmL94CktNTyzCU4ziuSsE4AoJtKtJPT4o0JpbpQEStgwHWCrfyGHnarg8cpyisnWtMBAXRqYn3ZyHabCoTE6Rg836tC7TeBqxr0c01+lPEdvifHiZoAPB+Pf3gLBa6vsEP6ChfI3/V2TDMZj1k26tGTn+Eerebs0H1aZRWvGy5HjxkDOiFjHmSMkLPoRvR2PRFnJqRpxh0pnWcheDzpmwrgSyHxgD7W2N8g+GWJ+9hX8JzVYqfzayAVNDxQgBEYztu1Yex11WY9JnC1 On Fri, 23 Oct 2026 17:55:29 +0200 Jerome Marchand wrote: > On ppc64 with CONFIG_TRACE_IRQFLAGS enabled, the ring buffer code can > enter in an infinite recursion loop. > > The problem occurs because some PowerPC's local_t operations > (local_inc/dec in particular) use powerpc_local_irq_pmu_save/restore() > which call trace_hardirqs_on/off() to generate trace events. This > creates a recursion loop: > > ring_buffer_unlock_commit() > rb_commit() > local_inc(&cpu_buffer->entries) > powerpc_local_irq_pmu_save() > trace_hardirqs_off() > trace event => ring_buffer_unlock_commit() > [INFINITE RECURSION] Hmm, the ring buffer has recursion protection that should prevent this. My question is, why didn't that work? Yes, I agree with the patch to not have local_inc/dec() call anything that can be traced, but if this caused an infinite recursion, there's a bug in the ring buffer code I want fixed too. The ring buffer has a trace_recursive_lock() that will allow one level of recursion and then prevents new commits from happening. The trace_recursive_unlock() is called after the rb_commit(). Why did the rb_commit() allow an infinite recursion? -- Steve