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SubjectRe: [PATCH 6/6] tracing: Change remove_event_file_dir() to clear "d_subdirs"->i_private
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On Tue, 2013-07-23 at 22:59 +0200, Oleg Nesterov wrote:
> Change remove_event_file_dir() ->i_private for every file we
> are going to remove.
>
> 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.

Hmm, but this patch opens up that race right? We remove the tr ref
counter updates here.

>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> kernel/trace/trace_events.c | 40 ++++++++--------------------------------
> 1 files changed, 8 insertions(+), 32 deletions(-)
>
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 3ae037c..298e4fa 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -428,42 +428,19 @@ 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;

Need space here.

> + /* ->i_mutex is not needed, nodody can create/remove a file */

"nodody" ;-)

-- Steve

> + list_for_each_entry(child, &dir->d_subdirs, d_u.d_child)
> + child->d_inode->i_private = NULL;
> +
> list_del(&file->list);
> - debugfs_remove_recursive(file->dir);
> + debugfs_remove_recursive(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
> @@ -1274,10 +1251,9 @@ 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,
> };
>




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