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Subject[for-next-3.11][PATCH 6/8] tracing: Change remove_event_file_dir() to clear "d_subdirs"->i_private
From: Oleg Nesterov <oleg@redhat.com>

Change remove_event_file_dir() to clear ->i_private for every
file we are going to remove.

We need to check file->dir != NULL because event_create_dir()
can fail. debugfs_remove_recursive(NULL) is fine but the patch
moves it under the same check anyway for readability.

spin_lock(d_lock) and "d_inode != NULL" check are not needed
afaics, but I do not understand this code enough.

tracing_open_generic_file() and tracing_release_generic_file()
can go away, ftrace_enable_fops and ftrace_event_filter_fops()
use tracing_open_generic() but only to check tracing_disabled.

This fixes all races with event_remove() or instance_delete().
f_op->read/write/whatever can never use the freed file/call,
all event/* files were changed to check and use ->i_private
under event_mutex.

Note: this doesn't not fix other problems, event_remove() can
destroy the active ftrace_event_call, we need more changes but
those changes are completely orthogonal.

Link: http://lkml.kernel.org/r/20130728183527.GB16723@redhat.com

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace_events.c | 47 ++++++++++++++-----------------------------
1 file changed, 15 insertions(+), 32 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 05d647e..a67c913 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -428,42 +428,26 @@ static void *event_file_data(struct file *filp)

static void remove_event_file_dir(struct ftrace_event_file *file)
{
+ struct dentry *dir = file->dir;
+ struct dentry *child;
+
+ if (dir) {
+ spin_lock(&dir->d_lock); /* probably unneeded */
+ list_for_each_entry(child, &dir->d_subdirs, d_u.d_child) {
+ if (child->d_inode) /* probably unneeded */
+ child->d_inode->i_private = NULL;
+ }
+ spin_unlock(&dir->d_lock);
+
+ debugfs_remove_recursive(dir);
+ }
+
list_del(&file->list);
- debugfs_remove_recursive(file->dir);
remove_subsystem(file->system);
kmem_cache_free(file_cachep, file);
}

/*
- * Open and update trace_array ref count.
- * Must have the current trace_array passed to it.
- */
-static int tracing_open_generic_file(struct inode *inode, struct file *filp)
-{
- struct ftrace_event_file *file = inode->i_private;
- struct trace_array *tr = file->tr;
- int ret;
-
- if (trace_array_get(tr) < 0)
- return -ENODEV;
-
- ret = tracing_open_generic(inode, filp);
- if (ret < 0)
- trace_array_put(tr);
- return ret;
-}
-
-static int tracing_release_generic_file(struct inode *inode, struct file *filp)
-{
- struct ftrace_event_file *file = inode->i_private;
- struct trace_array *tr = file->tr;
-
- trace_array_put(tr);
-
- return 0;
-}
-
-/*
* __ftrace_set_clr_event(NULL, NULL, NULL, set) will set/unset all events.
*/
static int
@@ -1281,10 +1265,9 @@ static const struct file_operations ftrace_set_event_fops = {
};

static const struct file_operations ftrace_enable_fops = {
- .open = tracing_open_generic_file,
+ .open = tracing_open_generic,
.read = event_enable_read,
.write = event_enable_write,
- .release = tracing_release_generic_file,
.llseek = default_llseek,
};

--
1.7.10.4



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