This is a note to let you know that I've just added the patch titled
tracing: Introduce trace_create_cpu_file() and
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-introduce-trace_create_cpu_file-and.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 649e9c70da6bfbeb563193a35d3424a5aa7c0d38 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Date: Tue, 23 Jul 2013 17:25:54 +0200
Subject: tracing: Introduce trace_create_cpu_file() and
tracing_get_cpu()
From: Oleg Nesterov <oleg@xxxxxxxxxx>
commit 649e9c70da6bfbeb563193a35d3424a5aa7c0d38 upstream.
Every "file_operations" used by tracing_init_debugfs_percpu is buggy.
f_op->open/etc does:
1. struct trace_cpu *tc = inode->i_private;
struct trace_array *tr = tc->tr;
2. trace_array_get(tr) or fail;
3. do_something(tc);
But tc (and tr) can be already freed before trace_array_get() is called.
And it doesn't matter whether this file is per-cpu or it was created by
init_tracer_debugfs(), free_percpu() or kfree() are equally bad.
Note that even 1. is not safe, the freed memory can be unmapped. But even
if it was safe trace_array_get() can wrongly succeed if we also race with
the next new_instance_create() which can re-allocate the same tr, or tc
was overwritten and ->tr points to the valid tr. In this case 3. uses the
freed/reused memory.
Add the new trivial helper, trace_create_cpu_file() which simply calls
trace_create_file() and encodes "cpu" in "struct inode". Another helper,
tracing_get_cpu() will be used to read cpu_nr-or-RING_BUFFER_ALL_CPUS.
The patch abuses ->i_cdev to encode the number, it is never used unless
the file is S_ISCHR(). But we could use something else, say, i_bytes or
even ->d_fsdata. In any case this hack is hidden inside these 2 helpers,
it would be trivial to change them if needed.
This patch only changes tracing_init_debugfs_percpu() to use the new
trace_create_cpu_file(), the next patches will change file_operations.
Note: tracing_get_cpu(inode) is always safe but you can't trust the
result unless trace_array_get() was called, without trace_types_lock
which acts as a barrier it can wrongly return RING_BUFFER_ALL_CPUS.
Link: http://lkml.kernel.org/r/20130723152554.GA23710@xxxxxxxxxx
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/trace/trace.c | 50 ++++++++++++++++++++++++++++++++++++--------------
1 file changed, 36 insertions(+), 14 deletions(-)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2834,6 +2834,17 @@ static int s_show(struct seq_file *m, vo
return 0;
}
+/*
+ * Should be used after trace_array_get(), trace_types_lock
+ * ensures that i_cdev was already initialized.
+ */
+static inline int tracing_get_cpu(struct inode *inode)
+{
+ if (inode->i_cdev) /* See trace_create_cpu_file() */
+ return (long)inode->i_cdev - 1;
+ return RING_BUFFER_ALL_CPUS;
+}
+
static const struct seq_operations tracer_seq_ops = {
.start = s_start,
.next = s_next,
@@ -5521,6 +5532,17 @@ static struct dentry *tracing_dentry_per
return tr->percpu_dir;
}
+static struct dentry *
+trace_create_cpu_file(const char *name, umode_t mode, struct dentry *parent,
+ void *data, long cpu, const struct file_operations *fops)
+{
+ struct dentry *ret = trace_create_file(name, mode, parent, data, fops);
+
+ if (ret) /* See tracing_get_cpu() */
+ ret->d_inode->i_cdev = (void *)(cpu + 1);
+ return ret;
+}
+
static void
tracing_init_debugfs_percpu(struct trace_array *tr, long cpu)
{
@@ -5540,28 +5562,28 @@ tracing_init_debugfs_percpu(struct trace
}
/* per cpu trace_pipe */
- trace_create_file("trace_pipe", 0444, d_cpu,
- (void *)&data->trace_cpu, &tracing_pipe_fops);
+ trace_create_cpu_file("trace_pipe", 0444, d_cpu,
+ &data->trace_cpu, cpu, &tracing_pipe_fops);
/* per cpu trace */
- trace_create_file("trace", 0644, d_cpu,
- (void *)&data->trace_cpu, &tracing_fops);
+ trace_create_cpu_file("trace", 0644, d_cpu,
+ &data->trace_cpu, cpu, &tracing_fops);
- trace_create_file("trace_pipe_raw", 0444, d_cpu,
- (void *)&data->trace_cpu, &tracing_buffers_fops);
+ trace_create_cpu_file("trace_pipe_raw", 0444, d_cpu,
+ &data->trace_cpu, cpu, &tracing_buffers_fops);
- trace_create_file("stats", 0444, d_cpu,
- (void *)&data->trace_cpu, &tracing_stats_fops);
+ trace_create_cpu_file("stats", 0444, d_cpu,
+ &data->trace_cpu, cpu, &tracing_stats_fops);
- trace_create_file("buffer_size_kb", 0444, d_cpu,
- (void *)&data->trace_cpu, &tracing_entries_fops);
+ trace_create_cpu_file("buffer_size_kb", 0444, d_cpu,
+ &data->trace_cpu, cpu, &tracing_entries_fops);
#ifdef CONFIG_TRACER_SNAPSHOT
- trace_create_file("snapshot", 0644, d_cpu,
- (void *)&data->trace_cpu, &snapshot_fops);
+ trace_create_cpu_file("snapshot", 0644, d_cpu,
+ &data->trace_cpu, cpu, &snapshot_fops);
- trace_create_file("snapshot_raw", 0444, d_cpu,
- (void *)&data->trace_cpu, &snapshot_raw_fops);
+ trace_create_cpu_file("snapshot_raw", 0444, d_cpu,
+ &data->trace_cpu, cpu, &snapshot_raw_fops);
#endif
}
Patches currently in stable-queue which might be from oleg@xxxxxxxxxx are
queue-3.10/tracing-introduce-trace_create_cpu_file-and.patch
queue-3.10/tracing-change-tracing_fops-snapshot_fops-to-rely-on-tracing_get_cpu.patch
queue-3.10/tracing-change-tracing_buffers_fops-to-rely-on-tracing_get_cpu.patch
queue-3.10/tracing-change-tracing_stats_fops-to-rely-on.patch
queue-3.10/tracing-change-tracing_pipe_fops-to-rely-on-tracing_get_cpu.patch
queue-3.10/tracing-change-tracing_entries_fops-to-rely-on-tracing_get_cpu.patch
queue-3.10/tracing-turn-event-id-i_private-into-call-event.type.patch
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