>>>>> " " == Dipankar Sarma <dipankar@in.ibm.com> writes:
>> Look at all those functions that take dcache_lock, and then
>> test
>> dentry-> d_count. Unless I'm missing something here, your
>> d_lookup() clearly has them all screwed, no?
> Not necessarily. One example is the fact that d_lookup() can
> only increase d_count. Besides, dput() decrements d_count
> without dcache_lock, so I am not sure holding dcache_lock
> during d_count test buys you much.
Wrong. Look at the VFS code. In all cases the test is of the form.
spin_lock(&dcache_lock);
/* Are we the sole users of this dentry */
if (atomic_read(&dentry->d_count) == 1) {
/* Yes - do some operation */
}
Knowing that d_lookup() can *increase* d_count is not a plus here. The
whole idea is to have a test for sole use.
In most cases, the "do some operation" above is
d_drop(dentry);
in order (for instance) to ensure that nobody else can look up this
dentry while we're working on it (e.g. rename or unlink,...).
Your d_lookup() screws the above example of code which you can find in
any number of VFS functions. dput(), d_delete(), d_invalidate(),
d_prune_aliases(), prune_dcache(), shrink_dcache_sb() are but a few
functions that rely on the above code snippet working to keep
d_lookup() from intruding.
Cheers,
Trond
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This archive was generated by hypermail 2b29 : Sun Jun 15 2003 - 22:00:35 EST