On Mon, 9 Jul 2007 14:47:45 +0100
Alan Cox <[EMAIL PROTECTED]> wrote:
> The locking is only done for lseek so this isn't a big change. All the
> other operations are thrown at the arch specific lower layers for locking
> handling without the file pointer being directly exposed.
>
> Signed-off-by: Alan Cox <[EMAIL PROTECTED]>
>
> diff -u --new-file --recursive --exclude-from /usr/src/exclude
> linux.vanilla-2.6.22-rc6-mm1/drivers/char/generic_nvram.c
> linux-2.6.22-rc6-mm1/drivers/char/generic_nvram.c
> --- linux.vanilla-2.6.22-rc6-mm1/drivers/char/generic_nvram.c 2007-07-02
> 20:47:23.000000000 +0100
> +++ linux-2.6.22-rc6-mm1/drivers/char/generic_nvram.c 2007-07-09
> 12:05:06.786669552 +0100
> @@ -30,7 +30,7 @@
>
> static loff_t nvram_llseek(struct file *file, loff_t offset, int origin)
> {
> - lock_kernel();
> + mutex_lock(&file->f_path.dentry->d_inode->i_mutex);
> switch (origin) {
> case 1:
> offset += file->f_pos;
> @@ -44,7 +44,7 @@
> return -EINVAL;
> }
> file->f_pos = offset;
> - unlock_kernel();
> + mutex_unlock(&file->f_path.dentry->d_inode->i_mutex);
> return file->f_pos;
> }
>
You left an unlock_kernel() on the error path, thus introducing a deadly
bug.
Can we just use generic_file_llseek() in here? afacit that simply requires
that i_size have the correct value. Does it?
generic_file_llseek() uses file->f_mapping->host->i_mutex which is
equivalent for this file, but we might as well be consistent.
While we're there, we can do s/magic numbers/standard symbols/.
And we can fix the remaining race in there by reading f_pos while holding
the mutex, not after having dropped it.
End result:
static loff_t nvram_llseek(struct file *file, loff_t offset, int origin)
{
struct inode *inode = file->f_mapping->host;
mutex_lock(&inode->i_mutex);
switch (origin) {
case SEEK_CUR:
offset += file->f_pos;
break;
case SEEK_END:
offset += NVRAM_SIZE;
break;
}
if (offset < 0) {
offset = -EINVAL;
goto out;
}
file->f_pos = offset;
out:
mutex_unlock(&inode->i_mutex);
return offset;
}
-
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