From nobody Mon Feb 9 09:09:32 2026 Received: from mail-wm1-f73.google.com (mail-wm1-f73.google.com [209.85.128.73]) (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 9676B53398 for ; Tue, 23 Apr 2024 23:27:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713914870; cv=none; b=ZO9hqEByimEEqAZWmXap0h43LodgV/zOVeXSFMN+j44Gud6WyTqPDmpc+2UrZhTVN4VcqC/XED9hKeF7qWx0PPM1P48/iONvWW5dDMErRcKwuuvF1WRfOFOpe2Xs+IkWMfUwtN+lgF0Lrj6vYlhRsekqSIoKQc/tx1DrXPx40yY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713914870; c=relaxed/simple; bh=VhRUrMgDXvxrbFcK977T8yS4Vw+MmwCzKPPOBPrfvio=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=UwGWl2pa8HiFlGfyFywMaOtUUFs3KVqMzlMxu9bfHIt8qCcYEhwRbJICHLyuxlVyIYgK9+qpmXzmYo6fa1nLq9aNZz9E2HKvbvg7CQgCXqD9ehmJFU4h0axD+0G/eC2XwBizzBEqP9Yta+cOA2iDbVBtmT9swFU7JhH0qeF4asE= 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=gV79sV/w; arc=none smtp.client-ip=209.85.128.73 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="gV79sV/w" Received: by mail-wm1-f73.google.com with SMTP id 5b1f17b1804b1-417fb8195d7so29796885e9.0 for ; Tue, 23 Apr 2024 16:27:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1713914867; x=1714519667; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=kaFaT9yjXtresVS5HFOg4DBcxHZeTWd1pZVR5Za+Mxc=; b=gV79sV/wpw+PwVFufPOBxghtSO+aHsjJ3kOxTNtnQakAQzPxTh6S3mF6Hi8B8bXR8y dDpK0niANFmAL+I1ERO11b1Y9dObETpYysa4sguhEi6jk6X7ujqmCMIr60FJs6Rey0ZJ py2YODRSnzk76H0xjNGUs0V76p+9xHguzuwM/jhHeJdKpy/SfT2nEJNP34k7zqxgjQNQ 5zKxPnk60vQ2IQvmzRjmHa+k87uygH+/t0GBO1kvr48UPXvpXmmKQGphd7AbQdti1J5d a9gUsSzA4+fSBH8SvvHNHcSrMD7vTuABwW2swr1E1Tr+2l5gUHDdMfIZr+PE9ZiEqEtS nnTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713914867; x=1714519667; h=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; bh=kaFaT9yjXtresVS5HFOg4DBcxHZeTWd1pZVR5Za+Mxc=; b=f6LGKa9lRgvhXds+5jKGIo/3iv1CJfPS5WEqNxJF/NaIU5j333j25vpzK900vOvvvu sTXFjaaZ+IevSuxsfx/au8EOzLIk71+u2l1LaRyCeuuvGAzgiR5HaSKhKKve3h6pSXm0 t1eqd9tqd5GXkRBv5g25QMx/2Pgv2Ex0BovSb+IKNz0TIfjqja5BIHDXc67k7apJOgA6 hORLsLSAFCaO/rePRnrpl5VftqiEHJvaI/ob1EwxAtwY2iqydLZGIv+QHhwistoSK9Ow dSsvQsSy8fKEwVaD0Nh2nXcbq3Jju/kaEwhHv/gX+4pdhEydWD/gOLq8OM2yhiYXbV8B B+ew== X-Forwarded-Encrypted: i=1; AJvYcCU6G8IXxb00veuarXBV0t4mo8O3Ng1xk6OsuoApUTRRCa68tLn5BeFUS/nxJGXQdi286G3aHS7/ttHUUcJbBTSuAMFbgIxk4yuTpOil X-Gm-Message-State: AOJu0Yz3eUOHjdoZzV+77k8TGQbQf9lFQrSeX2d3Cx+ZZSFwftGH5Lep aDSOOmzHCHcyNVUonIOnxV3D1GoFZHNgQwbJzQ6jrt2QyZxm7PdYoJWwt4+1hFOHf5ZvI9+PG2d PwBmlpzrTRQx+WKn45A== X-Google-Smtp-Source: AGHT+IFCDABCADdFLnD0phykkbD9Gu5AIQBZ62UxA/EhQAKHMu7J7egaT2rm+tUe6aiIMaJ0/Tc/k/iDgGFOOjAe X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a05:600c:5352:b0:41a:3485:19c4 with SMTP id hi18-20020a05600c535200b0041a348519c4mr3395wmb.3.1713914867196; Tue, 23 Apr 2024 16:27:47 -0700 (PDT) Date: Wed, 24 Apr 2024 00:27:26 +0100 In-Reply-To: <20240423232728.1492340-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240423232728.1492340-1-vdonnefort@google.com> X-Mailer: git-send-email 2.44.0.769.g3c40516874-goog Message-ID: <20240423232728.1492340-4-vdonnefort@google.com> Subject: [PATCH v21 3/5] tracing: Allow user-space mapping of the ring-buffer From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, rdunlap@infradead.org, rppt@kernel.org, david@redhat.com, Vincent Donnefort , linux-mm@kvack.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently, user-space extracts data from the ring-buffer via splice, which is handy for storage or network sharing. However, due to splice limitations, it is imposible to do real-time analysis without a copy. A solution for that problem is to let the user-space map the ring-buffer directly. The mapping is exposed via the per-CPU file trace_pipe_raw. The first element of the mapping is the meta-page. It is followed by each subbuffer constituting the ring-buffer, ordered by their unique page ID: * Meta-page -- include/uapi/linux/trace_mmap.h for a description * Subbuf ID 0 * Subbuf ID 1 ... It is therefore easy to translate a subbuf ID into an offset in the mapping: reader_id =3D meta->reader->id; reader_offset =3D meta->meta_page_size + reader_id * meta->subbuf_size; When new data is available, the mapper must call a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to point to the next reader containing unread data. Mapping will prevent snapshot and buffer size modifications. CC: Signed-off-by: Vincent Donnefort diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mma= p.h index b682e9925539..bd1066754220 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -43,4 +43,6 @@ struct trace_buffer_meta { __u64 Reserved2; }; =20 +#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1) + #endif /* _TRACE_MMAP_H_ */ diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 233d1af39fff..a35e7f598233 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -1191,6 +1191,12 @@ static void tracing_snapshot_instance_cond(struct tr= ace_array *tr, return; } =20 + if (tr->mapped) { + trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n"); + trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n"); + return; + } + local_irq_save(flags); update_max_tr(tr, current, smp_processor_id(), cond_data); local_irq_restore(flags); @@ -1323,7 +1329,7 @@ static int tracing_arm_snapshot_locked(struct trace_a= rray *tr) lockdep_assert_held(&trace_types_lock); =20 spin_lock(&tr->snapshot_trigger_lock); - if (tr->snapshot =3D=3D UINT_MAX) { + if (tr->snapshot =3D=3D UINT_MAX || tr->mapped) { spin_unlock(&tr->snapshot_trigger_lock); return -EBUSY; } @@ -6068,7 +6074,7 @@ static void tracing_set_nop(struct trace_array *tr) { if (tr->current_trace =3D=3D &nop_trace) return; -=09 + tr->current_trace->enabled--; =20 if (tr->current_trace->reset) @@ -8194,15 +8200,32 @@ tracing_buffers_splice_read(struct file *file, loff= _t *ppos, return ret; } =20 -/* An ioctl call with cmd 0 to the ring buffer file will wake up all waite= rs */ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, uns= igned long arg) { struct ftrace_buffer_info *info =3D file->private_data; struct trace_iterator *iter =3D &info->iter; + int err; + + if (cmd =3D=3D TRACE_MMAP_IOCTL_GET_READER) { + if (!(file->f_flags & O_NONBLOCK)) { + err =3D ring_buffer_wait(iter->array_buffer->buffer, + iter->cpu_file, + iter->tr->buffer_percent, + NULL, NULL); + if (err) + return err; + } =20 - if (cmd) - return -ENOIOCTLCMD; + return ring_buffer_map_get_reader(iter->array_buffer->buffer, + iter->cpu_file); + } else if (cmd) { + return -ENOTTY; + } =20 + /* + * An ioctl call with cmd 0 to the ring buffer file will wake up all + * waiters + */ mutex_lock(&trace_types_lock); =20 /* Make sure the waiters see the new wait_index */ @@ -8214,6 +8237,76 @@ static long tracing_buffers_ioctl(struct file *file,= unsigned int cmd, unsigned return 0; } =20 +#ifdef CONFIG_TRACER_MAX_TRACE +static int get_snapshot_map(struct trace_array *tr) +{ + int err =3D 0; + + /* + * Called with mmap_lock held. lockdep would be unhappy if we would now + * take trace_types_lock. Instead use the specific + * snapshot_trigger_lock. + */ + spin_lock(&tr->snapshot_trigger_lock); + + if (tr->snapshot || tr->mapped =3D=3D UINT_MAX) + err =3D -EBUSY; + else + tr->mapped++; + + spin_unlock(&tr->snapshot_trigger_lock); + + /* Wait for update_max_tr() to observe iter->tr->mapped */ + if (tr->mapped =3D=3D 1) + synchronize_rcu(); + + return err; + +} +static void put_snapshot_map(struct trace_array *tr) +{ + spin_lock(&tr->snapshot_trigger_lock); + if (!WARN_ON(!tr->mapped)) + tr->mapped--; + spin_unlock(&tr->snapshot_trigger_lock); +} +#else +static inline int get_snapshot_map(struct trace_array *tr) { return 0; } +static inline void put_snapshot_map(struct trace_array *tr) { } +#endif + +static void tracing_buffers_mmap_close(struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info =3D vma->vm_file->private_data; + struct trace_iterator *iter =3D &info->iter; + + WARN_ON(ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file)); + put_snapshot_map(iter->tr); +} + +static const struct vm_operations_struct tracing_buffers_vmops =3D { + .close =3D tracing_buffers_mmap_close, +}; + +static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *= vma) +{ + struct ftrace_buffer_info *info =3D filp->private_data; + struct trace_iterator *iter =3D &info->iter; + int ret =3D 0; + + ret =3D get_snapshot_map(iter->tr); + if (ret) + return ret; + + ret =3D ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file, vma); + if (ret) + put_snapshot_map(iter->tr); + + vma->vm_ops =3D &tracing_buffers_vmops; + + return ret; +} + static const struct file_operations tracing_buffers_fops =3D { .open =3D tracing_buffers_open, .read =3D tracing_buffers_read, @@ -8223,6 +8316,7 @@ static const struct file_operations tracing_buffers_f= ops =3D { .splice_read =3D tracing_buffers_splice_read, .unlocked_ioctl =3D tracing_buffers_ioctl, .llseek =3D no_llseek, + .mmap =3D tracing_buffers_mmap, }; =20 static ssize_t diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 64450615ca0c..749a182dab48 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -336,6 +336,7 @@ struct trace_array { bool allocated_snapshot; spinlock_t snapshot_trigger_lock; unsigned int snapshot; + unsigned int mapped; unsigned long max_latency; #ifdef CONFIG_FSNOTIFY struct dentry *d_max_latency; --=20 2.44.0.769.g3c40516874-goog