From 20c8928abe70e204bd077ab6cfe23002d7788983 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Wed, 6 May 2009 10:33:45 +0800 Subject: tracing/events: fix concurrent access to ftrace_events list A module will add/remove its trace events when it gets loaded/unloaded, so the ftrace_events list is not "const", and concurrent access needs to be protected. This patch thus fixes races between loading/unloding modules and read 'available_events' or read/write 'set_event', etc. Below shows how to reproduce the race: # for ((; ;)) { cat /mnt/tracing/available_events; } > /dev/null & # for ((; ;)) { insmod trace-events-sample.ko; rmmod sample; } & After a while: BUG: unable to handle kernel paging request at 0010011c IP: [] t_next+0x1b/0x2d ... Call Trace: [] ? seq_read+0x217/0x30d [] ? seq_read+0x0/0x30d [] ? vfs_read+0x8f/0x136 [] ? sys_read+0x40/0x65 [] ? sysenter_do_call+0x12/0x36 [ Impact: fix races when concurrent accessing ftrace_events list ] Signed-off-by: Li Zefan Acked-by: Steven Rostedt Acked-by: Frederic Weisbecker Cc: Tom Zanussi Cc: Peter Zijlstra LKML-Reference: <4A00F709.3080800@cn.fujitsu.com> Signed-off-by: Ingo Molnar --- kernel/trace/trace_events.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) (limited to 'kernel/trace/trace_events.c') diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index f251a150e75..8d579ff2361 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -21,7 +21,7 @@ #define TRACE_SYSTEM "TRACE_SYSTEM" -static DEFINE_MUTEX(event_mutex); +DEFINE_MUTEX(event_mutex); LIST_HEAD(ftrace_events); @@ -80,6 +80,7 @@ static void ftrace_clear_events(void) { struct ftrace_event_call *call; + mutex_lock(&event_mutex); list_for_each_entry(call, &ftrace_events, list) { if (call->enabled) { @@ -87,6 +88,7 @@ static void ftrace_clear_events(void) call->unregfunc(); } } + mutex_unlock(&event_mutex); } static void ftrace_event_enable_disable(struct ftrace_event_call *call, @@ -274,6 +276,9 @@ t_next(struct seq_file *m, void *v, loff_t *pos) static void *t_start(struct seq_file *m, loff_t *pos) { + mutex_lock(&event_mutex); + if (*pos == 0) + m->private = ftrace_events.next; return t_next(m, NULL, pos); } @@ -303,6 +308,9 @@ s_next(struct seq_file *m, void *v, loff_t *pos) static void *s_start(struct seq_file *m, loff_t *pos) { + mutex_lock(&event_mutex); + if (*pos == 0) + m->private = ftrace_events.next; return s_next(m, NULL, pos); } @@ -319,12 +327,12 @@ static int t_show(struct seq_file *m, void *v) static void t_stop(struct seq_file *m, void *p) { + mutex_unlock(&event_mutex); } static int ftrace_event_seq_open(struct inode *inode, struct file *file) { - int ret; const struct seq_operations *seq_ops; if ((file->f_mode & FMODE_WRITE) && @@ -332,13 +340,7 @@ ftrace_event_seq_open(struct inode *inode, struct file *file) ftrace_clear_events(); seq_ops = inode->i_private; - ret = seq_open(file, seq_ops); - if (!ret) { - struct seq_file *m = file->private_data; - - m->private = ftrace_events.next; - } - return ret; + return seq_open(file, seq_ops); } static ssize_t -- cgit v1.2.3-70-g09d2