From d716ff71dd12bc6328f84a9ec1c3647daf01c827 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Mon, 15 Dec 2014 22:31:07 -0500 Subject: [PATCH] tracing: Remove taking of trace_types_lock in pipe files Taking the global mutex "trace_types_lock" in the trace_pipe files causes a bottle neck as most the pipe files can be read per cpu and there's no reason to serialize them. The current_trace variable was given a ref count and it can not change when the ref count is not zero. Opening the trace_pipe files will up the ref count (and decremented on close), so that the lock no longer needs to be taken when accessing the current_trace variable. Signed-off-by: Steven Rostedt --- kernel/trace/trace.c | 110 +++++++++++-------------------------------- 1 file changed, 28 insertions(+), 82 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ed3fba1d6570..7669b1f3234e 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4332,17 +4332,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) } trace_seq_init(&iter->seq); - - /* - * We make a copy of the current tracer to avoid concurrent - * changes on it while we are reading. - */ - iter->trace = kmalloc(sizeof(*iter->trace), GFP_KERNEL); - if (!iter->trace) { - ret = -ENOMEM; - goto fail; - } - *iter->trace = *tr->current_trace; + iter->trace = tr->current_trace; if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) { ret = -ENOMEM; @@ -4399,7 +4389,6 @@ static int tracing_release_pipe(struct inode *inode, struct file *file) free_cpumask_var(iter->started); mutex_destroy(&iter->mutex); - kfree(iter->trace); kfree(iter); trace_array_put(tr); @@ -4432,7 +4421,7 @@ tracing_poll_pipe(struct file *filp, poll_table *poll_table) return trace_poll(iter, filp, poll_table); } -/* Must be called with trace_types_lock mutex held. */ +/* Must be called with iter->mutex held. */ static int tracing_wait_pipe(struct file *filp) { struct trace_iterator *iter = filp->private_data; @@ -4477,7 +4466,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos) { struct trace_iterator *iter = filp->private_data; - struct trace_array *tr = iter->tr; ssize_t sret; /* return any leftover data */ @@ -4487,12 +4475,6 @@ tracing_read_pipe(struct file *filp, char __user *ubuf, trace_seq_init(&iter->seq); - /* copy the tracer to avoid using a global lock all around */ - mutex_lock(&trace_types_lock); - if (unlikely(iter->trace->name != tr->current_trace->name)) - *iter->trace = *tr->current_trace; - mutex_unlock(&trace_types_lock); - /* * Avoid more than one consumer on a single file descriptor * This is just a matter of traces coherency, the ring buffer itself @@ -4652,7 +4634,6 @@ static ssize_t tracing_splice_read_pipe(struct file *filp, .ops = &tracing_pipe_buf_ops, .spd_release = tracing_spd_release_pipe, }; - struct trace_array *tr = iter->tr; ssize_t ret; size_t rem; unsigned int i; @@ -4660,12 +4641,6 @@ static ssize_t tracing_splice_read_pipe(struct file *filp, if (splice_grow_spd(pipe, &spd)) return -ENOMEM; - /* copy the tracer to avoid using a global lock all around */ - mutex_lock(&trace_types_lock); - if (unlikely(iter->trace->name != tr->current_trace->name)) - *iter->trace = *tr->current_trace; - mutex_unlock(&trace_types_lock); - mutex_lock(&iter->mutex); if (iter->trace->splice_read) { @@ -5373,21 +5348,16 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, if (!count) return 0; - mutex_lock(&trace_types_lock); - #ifdef CONFIG_TRACER_MAX_TRACE - if (iter->snapshot && iter->tr->current_trace->use_max_tr) { - size = -EBUSY; - goto out_unlock; - } + if (iter->snapshot && iter->tr->current_trace->use_max_tr) + return -EBUSY; #endif if (!info->spare) info->spare = ring_buffer_alloc_read_page(iter->trace_buffer->buffer, iter->cpu_file); - size = -ENOMEM; if (!info->spare) - goto out_unlock; + return -ENOMEM; /* Do we have previous read data to read? */ if (info->read < PAGE_SIZE) @@ -5403,21 +5373,16 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, if (ret < 0) { if (trace_empty(iter)) { - if ((filp->f_flags & O_NONBLOCK)) { - size = -EAGAIN; - goto out_unlock; - } - mutex_unlock(&trace_types_lock); + if ((filp->f_flags & O_NONBLOCK)) + return -EAGAIN; + ret = wait_on_pipe(iter, false); - mutex_lock(&trace_types_lock); - if (ret) { - size = ret; - goto out_unlock; - } + if (ret) + return ret; + goto again; } - size = 0; - goto out_unlock; + return 0; } info->read = 0; @@ -5427,18 +5392,14 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, size = count; ret = copy_to_user(ubuf, info->spare + info->read, size); - if (ret == size) { - size = -EFAULT; - goto out_unlock; - } + if (ret == size) + return -EFAULT; + size -= ret; *ppos += size; info->read += size; - out_unlock: - mutex_unlock(&trace_types_lock); - return size; } @@ -5536,30 +5497,20 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, int entries, size, i; ssize_t ret = 0; - mutex_lock(&trace_types_lock); - #ifdef CONFIG_TRACER_MAX_TRACE - if (iter->snapshot && iter->tr->current_trace->use_max_tr) { - ret = -EBUSY; - goto out; - } + if (iter->snapshot && iter->tr->current_trace->use_max_tr) + return -EBUSY; #endif - if (splice_grow_spd(pipe, &spd)) { - ret = -ENOMEM; - goto out; - } + if (splice_grow_spd(pipe, &spd)) + return -ENOMEM; - if (*ppos & (PAGE_SIZE - 1)) { - ret = -EINVAL; - goto out; - } + if (*ppos & (PAGE_SIZE - 1)) + return -EINVAL; if (len & (PAGE_SIZE - 1)) { - if (len < PAGE_SIZE) { - ret = -EINVAL; - goto out; - } + if (len < PAGE_SIZE) + return -EINVAL; len &= PAGE_MASK; } @@ -5620,25 +5571,20 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, /* did we read anything? */ if (!spd.nr_pages) { if (ret) - goto out; + return ret; + + if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK)) + return -EAGAIN; - if ((file->f_flags & O_NONBLOCK) || (flags & SPLICE_F_NONBLOCK)) { - ret = -EAGAIN; - goto out; - } - mutex_unlock(&trace_types_lock); ret = wait_on_pipe(iter, true); - mutex_lock(&trace_types_lock); if (ret) - goto out; + return ret; goto again; } ret = splice_to_pipe(pipe, &spd); splice_shrink_spd(&spd); -out: - mutex_unlock(&trace_types_lock); return ret; } -- 2.20.1