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Date: Wed, 28 Jan 2009 13:24:15 -0500
From: Jeff Layton <jlayton@...hat.com>
To: Alexey Dobriyan <adobriyan@...il.com>
Cc: viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] proc: do PDE usecounting even for ->read_proc,
->write_proc
On Tue, 27 Jan 2009 02:31:51 +0300
Alexey Dobriyan <adobriyan@...il.com> wrote:
> Not exactly tested but one should get the idea.
>
>
>
> -----------------------------------------------
> struct proc_dir_entry::owner is going to be removed. Now it's only necessary
> to protect PDEs which are using ->read_proc, ->write_proc hooks.
>
> However, ->owner assignments are racy and make it very easy for someone to switch
> ->owner on live PDE (as some subsystems do) without fixing refcounts and so on.
>
> http://bugzilla.kernel.org/show_bug.cgi?id=12454
>
> So, ->owner is on death row.
>
> Proxy file operations exist already (proc_file_operations), just bump usecount
> when necessary.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
> fs/proc/generic.c | 48 ++++++++++++++++++++++++++++++++++++++----------
> fs/proc/inode.c | 2 +-
> fs/proc/internal.h | 1 +
> 3 files changed, 40 insertions(+), 11 deletions(-)
>
> diff --git a/fs/proc/generic.c b/fs/proc/generic.c
> index 5ee636a..65cc1ee 100644
> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -37,7 +37,7 @@ static int proc_match(int len, const char *name, struct proc_dir_entry *de)
> #define PROC_BLOCK_SIZE (PAGE_SIZE - 1024)
>
> static ssize_t
> -proc_file_read(struct file *file, char __user *buf, size_t nbytes,
> +__proc_file_read(struct file *file, char __user *buf, size_t nbytes,
> loff_t *ppos)
> {
> struct inode * inode = file->f_path.dentry->d_inode;
> @@ -183,19 +183,47 @@ proc_file_read(struct file *file, char __user *buf, size_t nbytes,
> }
>
> static ssize_t
> +proc_file_read(struct file *file, char __user *buf, size_t nbytes,
> + loff_t *ppos)
> +{
> + struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
> + ssize_t rv = -EIO;
> +
> + spin_lock(&pde->pde_unload_lock);
> + if (!pde->proc_fops) {
> + spin_unlock(&pde->pde_unload_lock);
> + return rv;
> + }
> + pde->pde_users++;
> + spin_unlock(&pde->pde_unload_lock);
> +
> + rv = __proc_file_read(file, buf, nbytes, ppos);
> +
> + pde_users_dec(pde);
> + return rv;
> +}
> +
> +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;
> -
> - dp = PDE(inode);
> -
> - if (!dp->write_proc)
> - return -EIO;
> + struct proc_dir_entry *pde = PDE(file->f_path.dentry->d_inode);
> + ssize_t rv = -EIO;
> +
> + if (pde->write_proc) {
> + spin_lock(&pde->pde_unload_lock);
> + if (!pde->proc_fops) {
> + spin_unlock(&pde->pde_unload_lock);
> + return rv;
> + }
> + pde->pde_users++;
> + spin_unlock(&pde->pde_unload_lock);
>
> - /* FIXME: does this routine need ppos? probably... */
> - return dp->write_proc(file, buffer, count, dp->data);
> + /* FIXME: does this routine need ppos? probably... */
> + rv = pde->write_proc(file, buffer, count, pde->data);
> + pde_users_dec(pde);
> + }
> + return rv;
> }
>
>
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
> index 0bbb937..7a55346 100644
> --- a/fs/proc/inode.c
> +++ b/fs/proc/inode.c
> @@ -127,7 +127,7 @@ static void __pde_users_dec(struct proc_dir_entry *pde)
> complete(pde->pde_unload_completion);
> }
>
> -static void pde_users_dec(struct proc_dir_entry *pde)
> +void pde_users_dec(struct proc_dir_entry *pde)
> {
> spin_lock(&pde->pde_unload_lock);
> __pde_users_dec(pde);
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index ab62ede..5b890ba 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -102,5 +102,6 @@ struct pde_opener {
> int (*release)(struct inode *, struct file *);
> struct list_head lh;
> };
> +void pde_users_dec(struct proc_dir_entry *pde);
>
> extern struct list_head proc_automounts;
I did some testing with this today and it seems to all work as expected. Nice work, Alexey.
Tested-by: Jeff Layton <jlayton@...hat.com>
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