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AJvYcCXHfjNdIPtNLzKqrt5ACw4yMjxzg40c1K7sNFaucOeRk5c2bd4unkOgAlEg8hCokAC9jNEgkgQC3/YR5cDWDLoxLlk= X-Gm-Message-State: AOJu0YyYky1N9rdPerRb/LfDDevBllz/8s/z8KFucSOLUxOwNJ+Jy+Hl w+gfyUf1+GME+ird36c5304/8wHZxpKWOCQmkiV7Gi6F/qqLH7wr1KdlRRe1QyQs+FkE1+l68g7 RaPxdLZoTJhpJV7y/mA== X-Google-Smtp-Source: AGHT+IFmbfbkyt1cuaCw7Z9TpcR3i/kvhX4wMWaVaTY6+kkbiriQkTVeu4WPHk+cGdtSa64MbF2oPERzDLCphX/v X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a05:600c:580a:b0:41b:e416:31e3 with SMTP id 5b1f17b1804b1-41fbd0b952cmr185995e9.3.1715349886925; Fri, 10 May 2024 07:04:46 -0700 (PDT) Date: Fri, 10 May 2024 15:04:32 +0100 In-Reply-To: <20240510140435.3550353-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20240510140435.3550353-1-vdonnefort@google.com> X-Mailer: git-send-email 2.45.0.118.g7fe29c98d7-goog Message-ID: <20240510140435.3550353-4-vdonnefort@google.com> Subject: [PATCH v23 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 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 7493F14005C X-Stat-Signature: r6gzgoethqakeazx5bb4sqn1ztzsymzi X-Rspam-User: X-HE-Tag: 1715349888-567948 X-HE-Meta: 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 K9WDEo4T 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 = meta->reader->id; reader_offset = 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_mmap.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; }; +#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 trace_array *tr, return; } + 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_array *tr) lockdep_assert_held(&trace_types_lock); spin_lock(&tr->snapshot_trigger_lock); - if (tr->snapshot == UINT_MAX) { + if (tr->snapshot == 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 == &nop_trace) return; - + tr->current_trace->enabled--; if (tr->current_trace->reset) @@ -8194,15 +8200,32 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, return ret; } -/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { struct ftrace_buffer_info *info = file->private_data; struct trace_iterator *iter = &info->iter; + int err; + + if (cmd == TRACE_MMAP_IOCTL_GET_READER) { + if (!(file->f_flags & O_NONBLOCK)) { + err = ring_buffer_wait(iter->array_buffer->buffer, + iter->cpu_file, + iter->tr->buffer_percent, + NULL, NULL); + if (err) + return err; + } - if (cmd) - return -ENOIOCTLCMD; + return ring_buffer_map_get_reader(iter->array_buffer->buffer, + iter->cpu_file); + } else if (cmd) { + return -ENOTTY; + } + /* + * An ioctl call with cmd 0 to the ring buffer file will wake up all + * waiters + */ mutex_lock(&trace_types_lock); /* 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; } +#ifdef CONFIG_TRACER_MAX_TRACE +static int get_snapshot_map(struct trace_array *tr) +{ + int err = 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 == UINT_MAX) + err = -EBUSY; + else + tr->mapped++; + + spin_unlock(&tr->snapshot_trigger_lock); + + /* Wait for update_max_tr() to observe iter->tr->mapped */ + if (tr->mapped == 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 = vma->vm_file->private_data; + struct trace_iterator *iter = &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 = { + .close = tracing_buffers_mmap_close, +}; + +static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info = filp->private_data; + struct trace_iterator *iter = &info->iter; + int ret = 0; + + ret = get_snapshot_map(iter->tr); + if (ret) + return ret; + + ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file, vma); + if (ret) + put_snapshot_map(iter->tr); + + vma->vm_ops = &tracing_buffers_vmops; + + return ret; +} + static const struct file_operations tracing_buffers_fops = { .open = tracing_buffers_open, .read = tracing_buffers_read, @@ -8223,6 +8316,7 @@ static const struct file_operations tracing_buffers_fops = { .splice_read = tracing_buffers_splice_read, .unlocked_ioctl = tracing_buffers_ioctl, .llseek = no_llseek, + .mmap = tracing_buffers_mmap, }; 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;