From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) (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 9DFFC3AB48F; Mon, 10 Aug 2026 22:42:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786401748; cv=none; b=aL3T03bGF2miVfjftCa3C8yAkn8waH8DjAlo+dhzENaVFWEsWIqmVt3do93p1jH6mEdCAU5G5T+i1f9QfLvuaHLMSv/H3wjtf5nBAhrdH25cIAGikYitvpjBAIK7XUeA9YXnaHzKPYNBTFaKqhMIMyKnzxm6U8NKUDF/0lptlwU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786401748; c=relaxed/simple; bh=7RoINJE4dbmabMMBpH1OQxD33IndvQyZfXs/LTop7vE=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=p263tMP8Kk6WJWbs2vsKKq6HHfyJUMiKzAMy1JKbt0xhYMbFmFv7e/VcSphDhDdMwLJc0sDMqyAs3g2TKr/G+pf0hd64YP9FFw1UtJx5uKPvuNfB8TKS4Ght0p/ok1h8+58rhaJgu71+dLsVo3vFo10Wkn/H1W8EvyDY11+jDJ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.14 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 13A4214029E; Mon, 10 Aug 2026 22:42:25 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf20.hostedemail.com (Postfix) with ESMTPA id 0F44C20025; Mon, 10 Aug 2026 22:42:22 +0000 (UTC) Date: Mon, 10 Aug 2026 18:42:16 -0400 From: Steven Rostedt To: Vincent Donnefort Cc: mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 06/18] tracing/remotes: Add dmesg tracefs file Message-ID: <20260810184216.3484cfd6@robin> In-Reply-To: <20260804140333.797210-7-vdonnefort@google.com> References: <20260804140333.797210-1-vdonnefort@google.com> <20260804140333.797210-7-vdonnefort@google.com> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspamout01 X-Rspamd-Queue-Id: 0F44C20025 X-Stat-Signature: tp5cghu49t5i784h5iq8kq356q65cd8q X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1//PoLAJORmJuh/4Sn43dzA1QgdKWLWnZo= X-HE-Tag: 1786401742-889997 X-HE-Meta: U2FsdGVkX1887pcpfHh0VeRjLffvaiXV57p/7Jrdlw2ZCak81yUqhCVs71BZufMMDJhZGv46IQ4S63xQA/shRfGFfV1uSECN+NHJz2ztjH7kjS7eeMGKSIJ4GSgiQUCK05MUoQNy+cBy9p+4YKYE8Lm0R7YR4BaanBkxk6Yz6RSKERFRI4vYOBXBzVwRXYkBGVzM6sbyisx98F/OR3XlspKCeLpepZk/xEnCrsJD0M49mHKBftNHhp+2kgQ8pn0c/PA3VR+RV6XEFBivpMrC1QqqwBciedkbXMVvCfbkSVFihY+XgcB8w3fEgjPVTstUpGq87OqU3Liu3SPWSh4bv9ZXqzg1ZMiKIBV7BxOT4lkR3tl7Xvzic3FesybuwkMvTZsha3fJuRz9KAzAxoo8+w== Adding Sashiko review: https://sashiko.dev/#/patchset/20260804140333.797210-2-vdonnefort%40google.com > --- Patch [6]: [PATCH v4 06/18] tracing/remotes: Add dmesg tracefs file --- > commit b6a4c19257d91807c612baa19691b2d602bb0670 > Author: Vincent Donnefort > > tracing/remotes: Add dmesg tracefs file > > When enabled, the dmesg tracefs file enables the redirection of all > events to dmesg. This is similar to tp_printk. > > > diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c > > index 1fbe2f3f20e99..58a38f3d49024 100644 > > --- a/kernel/trace/trace_remote.c > > +++ b/kernel/trace/trace_remote.c > > > [ ... ] > > > @@ -882,6 +908,87 @@ static const struct file_operations trace_fops = { > > .release = trace_release, > > }; > > > > +static bool trace_remote_do_dmesg(struct trace_remote *remote) > > +{ > > + struct trace_remote_iterator *iter = smp_load_acquire(&remote->dmesg); > > + unsigned int max_events = 1000; > > + > > + if (!iter) > > + return false; > > + > > + trace_remote_iter_read_start(iter); > > + > > + while (trace_remote_iter_read_event(iter)) { > > + trace_seq_init(&iter->seq); > > + > > + trace_remote_iter_print_event(iter); > > + trace_seq_putc(&iter->seq, 0); > > + if (!pr_info("%s", iter->seq.buffer)) > > If the remote trace event exceeds the PAGE_SIZE sequence buffer, does > trace_seq_putc() in trace_remote_do_dmesg() fail to append the null byte? > > Since iter->seq.buffer might not be null-terminated in this case, could this > lead to an out-of-bounds read when pr_info() prints the string? Yeah, we may want to have it be: if (!pr_info("%s", seq_buf_str(&iter->seq)) Which will make sure the buffer is nul terminated. > > This isn't a bug introduced by this patch, but the same pattern appears > to exist in the pre-existing trace_remote_panic_handler() with pr_emerg(). > > If the kernel is built with CONFIG_PRINTK disabled, pr_info() evaluates to 0. > > Will this cause the loop in trace_remote_do_dmesg() to break without calling > trace_remote_iter_move(), leaving the event unconsumed and permanently > stalling the workqueue? > > > + break; > > + > > + trace_remote_iter_move(iter); > > + > > + if (!(--max_events)) > > + break; > > + } > > + > > + trace_remote_iter_read_finished(iter); > > + > > + return !max_events; > > +} > > While reviewing this, I also noticed a pre-existing issue in trace_pipe_read() > when handling oversized events: > > kernel/trace/trace_remote.c:trace_pipe_read() { > ... > if (trace_remote_iter_print_event(iter)) { > iter->seq.seq.len = prev_len; > break; > } > ... > } > > This is a pre-existing issue, but if an oversized event causes > trace_remote_iter_print_event() to return -EOVERFLOW, will this break > the loop without calling trace_remote_iter_move()? > > Since the event is left unconsumed in the buffer, could this lead to an > uninterruptible infinite loop (hard lockup) when reading the trace pipe? I'll let you answer the above. -- Steve