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    SubjectRe: Two identical entries for "rtc" in /proc/devices
    Date
    On Saturday 15 September 2007, Andrew Morton wrote:
    > On Sat, 15 Sep 2007 11:50:21 -0700 David Brownell <david-b@pacbell.net> wrote:
    >
    > > > On Thu, 06 Sep 2007 18:23:22 -0400 Chuck Ebbert <cebbert@redhat.com> wrote:
    > > >
    > > > > # ls -li
    > > > > total 0
    > > > > 4026532007 -r--r--r-- 1 root root 0 Sep 6 18:18 nvram
    > > > > 4026532067 -r--r--r-- 1 root root 0 Sep 6 18:18 rtc
    > > > > 4026532067 -r--r--r-- 1 root root 0 Sep 6 18:18 rtc
    > > > > 4026532056 -rw-r--r-- 1 root root 0 Sep 6 18:18 snd-page-alloc
    > > >
    > > > ...
    > >
    > > Semes pretty clear that this must be procfs itself...
    > > when a filesystem sees a name in a directory, it should
    > > refuse to make another file with the same name. And it
    > > should *never* reuse inode numbers...
    >
    > ...
    >
    > procfs can reject the attempt to create the file, but the bottom line
    > is that two different callsites are trying to create the same file. One
    > of those callsites needs fixing?

    Both of those call sites have code to handle procfs rejecting
    the file creation; nothing to fix. And anyway, there's no way
    this is a *caller* bug!

    The missing step seems to be that proc_register() doesn't bother
    to check whether there's already an entry for that file. Which
    is what the appended *UNTESTED* patch does (it compiles though).

    - Dave

    --- g26.orig/fs/proc/generic.c 2007-09-18 22:08:44.000000000 -0700
    +++ g26/fs/proc/generic.c 2007-09-18 22:14:07.000000000 -0700
    @@ -521,10 +521,11 @@ static const struct inode_operations pro
    .setattr = proc_notify_change,
    };

    -static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp)
    +static int proc_register(struct proc_dir_entry *dir, struct proc_dir_entry *dp)
    {
    unsigned int i;
    -
    + struct proc_dir_entry *de;
    +
    i = get_inode_number();
    if (i == 0)
    return -EAGAIN;
    @@ -547,6 +548,16 @@ static int proc_register(struct proc_dir
    }

    spin_lock(&proc_subdir_lock);
    +
    + for (de = dir->subdir; de ; de = de->next) {
    + if (de->namelen != dp->namelen)
    + continue;
    + if (!memcmp(de->name, dp->name, de->namelen)) {
    + spin_unlock(&proc_subdir_lock);
    + return -EEXIST;
    + }
    + }
    +
    dp->next = dir->subdir;
    dp->parent = dir;
    dir->subdir = dp;
    -
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