On Sun, 11 Feb 2007 23:23:30 +0300 Alexey Dobriyan <[email protected]> wrote:
> [PATCH v4] Fix rmmod/read/write races in /proc entries
This:
static ssize_t
proc_file_write(struct file *file, const char __user *buffer,
size_t count, loff_t *ppos)
{
struct inode *inode = file->f_path.dentry->d_inode;
struct proc_dir_entry * dp;
ssize_t rv = -EIO;
dp = PDE(inode);
if (!dp->write_proc)
goto out;
spin_lock(&dp->pde_unload_lock);
if (!dp->proc_fops)
/*
* remove_proc_entry() marked PDE as "going away".
* No new writers allowed.
*/
goto out_unlock;
versus
spin_lock(&de->pde_unload_lock);
/*
* Stop accepting new readers/writers. If you're dynamically
* allocating ->proc_fops, save a pointer somewhere.
*/
de->proc_fops = NULL;
/* Wait until all existing readers/writers are done. */
if (de->pde_users > 0) {
struct completion c;
init_completion(&c);
if (!de->pde_unload_completion)
de->pde_unload_completion = &c;
spin_unlock(&de->pde_unload_lock);
spin_unlock(&proc_subdir_lock);
wait_for_completion(de->pde_unload_completion);
spin_lock(&proc_subdir_lock);
goto continue_removing;
}
spin_unlock(&de->pde_unload_lock);
<here>
...
<free de>
What prevents proc_file_write() from looking up and playing with this de in
<here>?
Also... lockdep wants this:
--- a/fs/proc/generic.c~fix-rmmod-read-write-races-in-proc-entries-fix
+++ a/fs/proc/generic.c
@@ -790,9 +790,8 @@ void remove_proc_entry(const char *name,
de->proc_fops = NULL;
/* Wait until all existing readers/writers are done. */
if (de->pde_users > 0) {
- struct completion c;
+ DECLARE_COMPLETION_ONSTACK(c);
- init_completion(&c);
if (!de->pde_unload_completion)
de->pde_unload_completion = &c;
_
-
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