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 <rostedt@goodmis.org>

1 files 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;
 }