From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1B68338D419 for ; Wed, 12 Aug 2026 16:13:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.70 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786551234; cv=none; b=mu/gkroAF6IrkjcngP6Mv9Z2iSkTUiWGIf4R6YMzkkHvPclbmM0MIodW7I43J1JNi4Jw6134cLLjezHtWbL4jsbjAIIqjpa6Ol4GBvsytojahzRtd+dDwm0Y5FaVM4N4r8hS6wcqj4F6g1GUGSBKB9d4Ui9z6s+WgQJ0jByfCKU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786551234; c=relaxed/simple; bh=nfs+emcg/ax3I41rHMf156WYOzcLQ04wy5rW5RCcq/A=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=UurNde4g96Z6ZLfSV82W5rC8IMGWb1QLu5i+vnrpY+JizZ+BO9s++Nr89y7QWhrYu+8ekHoQmyAT6i6k/4uEnx6lg4AGfj+l4SD/JYeS8UJWxvS7r8tj7iydfzBII8E5w1/8f9U7j6eaTpdZVRzaNqZuylL/3mrId/NRBcRL8Ag= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=Bb9NmY+m; arc=none smtp.client-ip=209.85.221.70 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Bb9NmY+m" Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-47fe85684b9so903457f8f.3 for ; Wed, 12 Aug 2026 09:13:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786551231; x=1787156031; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=7mQU2zGlqT46UqdzFFyK4d8sGbbDQ0hsX37gSyi0udk=; b=Bb9NmY+mDU64/yeiuu63j/fiSNRpipbroa2b1To1M1Htx+kYsRTdgkTWP0BEM21kq/ Nq4iddLecGl5cazKO5TTu6bPoYWF21u/ZBjaIUxaQwBhSmVirYg5N2m2qmk95zxFeq7k pespbvkGGMEJq145a2FqYIBSvHUvEl2J7HOVJTpKqSgYqwFxtP730L7aivHwRYBtP6YQ iyFx7m7gs1yr+CIGfGHXaKdAjTseAU4Bb22iT017DlM5I6UPEw8368DV4bDaAtujw1OU PjzxHMaxqvTJbwmwgifNxDQ311CKXVE03Hw0fpEGW8RlyJVdB2oZNy4JEm6C6AT82f/q k0hA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786551231; x=1787156031; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=7mQU2zGlqT46UqdzFFyK4d8sGbbDQ0hsX37gSyi0udk=; b=ekk54VkqN2fq/2dK48IPhd9RY4r/wE7vbuMpTMShrylISCHCggTWw3aTVlfgc3no/N AiYT/LJ+O9fTXJmYxmgi/zs45SIXWtFiTcK/EigocEoihzusdZXG/f7fm8FkFJ97KPjm esNiUyXEpsPfd07gmZvfEgSwD1hLQo3JIxFCwnRa7edLdt2ZaPdIZWrHjD+PewxyOZCg tfUDHDS2BhqTjp/NPb2HsGH/nLuREqv6+x0Nka0LUfhXG7tP/LKv1Tpmsm0kOhwBWFis +3LWk0RCD8BcfzOfiTGw6hkBPAeWFXmTzFJadeNKziV3QtZDBD9cUZ2RfawY1uKqNsRc VpBA== X-Forwarded-Encrypted: i=1; AHgh+RptapBvs0qA7VXjTATPjaBU2RAk3YbtLSR6zunUvoDwqwSf01udJ03m2D0cf2rKSeHaPuIjv5AqHYN9n8g=@vger.kernel.org X-Gm-Message-State: AOJu0YzctwQcvyLelDKkkXP7rqBlrpt5MHtl3Rg6FuO8IK6zpYOYC4lZ MTqnuLWs7CW2S/XYxLolpwfsMGnTPuu9GjLEh6FtRuhtQzMFmRgGzSki9YR5nxAwkHPo/VpUJ2s DehXxc21hbF8RmPrfA+akLQ== X-Received: from wmfu20.prod.google.com ([2002:a05:600c:1394:b0:493:d3c4:6a28]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:a04:b0:499:795a:c60b with SMTP id 5b1f17b1804b1-4997c170615mr74814755e9.19.1786551231055; Wed, 12 Aug 2026 09:13:51 -0700 (PDT) Date: Wed, 12 Aug 2026 17:13:28 +0100 In-Reply-To: <20260812161340.2417322-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260812161340.2417322-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.691.gc56d675ccc-goog Message-ID: <20260812161340.2417322-7-vdonnefort@google.com> Subject: [PATCH v5 06/18] tracing/remotes: Add dmesg tracefs file From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org, Vincent Donnefort Content-Type: text/plain; charset="UTF-8" When enabled, the dmesg tracefs file enables the redirection of all events to dmesg. This is similar to tp_printk. Signed-off-by: Vincent Donnefort diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 1fbe2f3f20e9..3a5e0d84c172 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -21,6 +21,7 @@ enum tri_type { TRI_CONSUMING, TRI_NONCONSUMING, + TRI_DMESG, }; struct trace_remote_iterator { @@ -43,6 +44,7 @@ struct trace_remote { void *priv; struct trace_buffer *trace_buffer; struct trace_buffer_desc *trace_buffer_desc; + struct trace_remote_iterator *dmesg; struct dentry *dentry; struct eventfs_inode *eventfs_root; struct eventfs_inode *eventfs_subdir; @@ -394,10 +396,15 @@ static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu) return 0; } +static bool trace_remote_do_dmesg(struct trace_remote *remote); + static void trace_remote_do_poll(struct trace_remote *remote) { + bool yield; + ring_buffer_poll_remote(remote->trace_buffer, RING_BUFFER_ALL_CPUS); - schedule_delayed_work(&remote->poll_work, msecs_to_jiffies(remote->poll_ms)); + yield = trace_remote_do_dmesg(remote); + schedule_delayed_work(&remote->poll_work, yield ? 0 : msecs_to_jiffies(remote->poll_ms)); } static void __poll_remote(struct work_struct *work) @@ -452,6 +459,14 @@ static struct trace_remote_iterator trace_seq_init(&iter->seq); switch (type) { + case TRI_DMESG: + /* only one dmesg iter allowed */ + if (WARN_ON_ONCE(remote->dmesg)) { + ret = -EBUSY; + break; + } + smp_store_release(&remote->dmesg, iter); + fallthrough; case TRI_CONSUMING: trace_remote_inc_poll(remote); break; @@ -486,6 +501,11 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter) lockdep_assert_held(&remote->lock); switch (iter->type) { + case TRI_DMESG: + WARN_ON_ONCE(remote->dmesg != iter); + smp_store_release(&remote->dmesg, NULL); + flush_delayed_work(&remote->poll_work); + fallthrough; case TRI_CONSUMING: trace_remote_dec_poll(remote); break; @@ -498,13 +518,24 @@ static void trace_remote_iter_free(struct trace_remote_iterator *iter) trace_remote_put(remote); } +static bool trace_remote_iter_is_consuming(struct trace_remote_iterator *iter) +{ + switch (iter->type) { + case TRI_CONSUMING: + case TRI_DMESG: + return true; + default: + return false; + } +} + static void trace_remote_iter_read_start(struct trace_remote_iterator *iter) { struct trace_remote *remote = iter->remote; int cpu = iter->cpu; /* Acquire global reader lock */ - if (cpu == RING_BUFFER_ALL_CPUS && iter->type == TRI_CONSUMING) + if (cpu == RING_BUFFER_ALL_CPUS && trace_remote_iter_is_consuming(iter)) down_write(&remote->reader_lock); else down_read(&remote->reader_lock); @@ -521,7 +552,7 @@ static void trace_remote_iter_read_start(struct trace_remote_iterator *iter) if (WARN_ON_ONCE(!remote->pcpu_reader_locks)) return; - if (iter->type == TRI_CONSUMING) + if (trace_remote_iter_is_consuming(iter)) down_write(&remote->pcpu_reader_locks[cpu]); else down_read(&remote->pcpu_reader_locks[cpu]); @@ -538,14 +569,14 @@ static void trace_remote_iter_read_finished(struct trace_remote_iterator *iter) * No need for the remote lock here, iter holds a reference on * remote->nr_readers */ - if (iter->type == TRI_CONSUMING) + if (trace_remote_iter_is_consuming(iter)) up_write(&remote->pcpu_reader_locks[cpu]); else up_read(&remote->pcpu_reader_locks[cpu]); } /* Release global reader lock */ - if (cpu == RING_BUFFER_ALL_CPUS && iter->type == TRI_CONSUMING) + if (cpu == RING_BUFFER_ALL_CPUS && trace_remote_iter_is_consuming(iter)) up_write(&remote->reader_lock); else up_read(&remote->reader_lock); @@ -562,10 +593,9 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long struct ring_buffer_event *rb_evt; struct ring_buffer_iter *rb_iter; - switch (iter->type) { - case TRI_CONSUMING: + if (trace_remote_iter_is_consuming(iter)) { return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events); - case TRI_NONCONSUMING: + } else { rb_iter = __get_rb_iter(iter, cpu); if (!rb_iter) return NULL; @@ -629,14 +659,10 @@ static void trace_remote_iter_move(struct trace_remote_iterator *iter) { struct trace_buffer *trace_buffer = iter->remote->trace_buffer; - switch (iter->type) { - case TRI_CONSUMING: + if (trace_remote_iter_is_consuming(iter)) ring_buffer_consume(trace_buffer, iter->evt_cpu, NULL, NULL); - break; - case TRI_NONCONSUMING: + else ring_buffer_iter_advance(__get_rb_iter(iter, iter->evt_cpu)); - break; - } } static struct remote_event *trace_remote_find_event(struct trace_remote *remote, unsigned short id); @@ -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", seq_buf_str(&iter->seq.seq))) + break; + + trace_remote_iter_move(iter); + + if (!(--max_events)) + break; + } + + trace_remote_iter_read_finished(iter); + + return !max_events; +} + +static int trace_remote_enable_dmesg(struct trace_remote *remote, bool enable) +{ + struct trace_remote_iterator *iter = remote->dmesg; + + lockdep_assert_held(&remote->lock); + + if (enable == !!iter) + return 0; + + if (enable) { + iter = trace_remote_iter(remote, RING_BUFFER_ALL_CPUS, TRI_DMESG); + if (IS_ERR(iter)) + return PTR_ERR(iter); + } else { + trace_remote_iter_free(remote->dmesg); + /* trace_remote_iter_free has reset remote->dmesg */ + } + + return 0; +} + +static ssize_t +dmesg_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *ppos) +{ + struct seq_file *seq = filp->private_data; + struct trace_remote *remote = seq->private; + bool val; + int ret; + + ret = kstrtobool_from_user(ubuf, cnt, &val); + if (ret) + return ret; + + guard(mutex)(&remote->lock); + + ret = trace_remote_enable_dmesg(remote, val); + if (ret) + return ret; + + return cnt; +} + +static int dmesg_show(struct seq_file *s, void *unused) +{ + struct trace_remote *remote = s->private; + + seq_printf(s, "%d\n", !!remote->dmesg); + + return 0; +} +DEFINE_TRACE_REMOTE_ATTRIBUTE(dmesg); + static int trace_remote_init_tracefs(const char *name, struct trace_remote *remote) { struct dentry *remote_d, *percpu_d, *d; @@ -922,6 +1029,10 @@ static int trace_remote_init_tracefs(const char *name, struct trace_remote *remo if (!d) goto err; + d = trace_create_file("dmesg", TRACEFS_MODE_WRITE, remote_d, remote, &dmesg_fops); + if (!d) + goto err; + percpu_d = tracefs_create_dir("per_cpu", remote_d); if (!percpu_d) { pr_err("Failed to create tracefs dir "TRACEFS_DIR"%s/per_cpu/\n", name); -- 2.55.0.691.gc56d675ccc-goog