On Thu, May 07, 2015 at 01:39:35PM -0400, Steven Rostedt wrote:
> I had them printed in my previous traces. The flags were 0x200088, and
> they were 0 just before the call.
Not dentry->d_flags, nd->flags. Most interesting part is bit 6 in those
(LOOKUP_RCU, 0x40).
As for creation... I think I see what might be going on:
A: finds a negative dentry, picks NULL ->d_inode from it and whatever
->d_seq it had.
B: d_instantiate(): sets ->d_inode non-NULL, ->d_flags accordingly and
bumps ->d_seq.
A: fetches ->d_flags, sees non-negative, assumes ->d_inode is non-NULL.
In reality, the last assumption should've been "->d_inode is non-NULL or
we have a stale ->d_seq and will end up discarding that fscker anyway".
Hmm... Smells like we ought to
a) in lookup_fast() turn
if (read_seqcount_retry(&dentry->d_seq, seq))
return -ECHILD;
into
if (unlikely(d_is_negative(dentry))) {
if (read_seqcount_retry(&dentry->d_seq, seq))
return -ECHILD;
else
return -ENOENT;
}
if (read_seqcount_retry(&dentry->d_seq, seq))
return -ECHILD;
and
if (likely(!err))
*inode = path->dentry->d_inode;
into
if (likely(!err)) {
*inode = path->dentry->d_inode;
if (unlikely(d_is_negative(dentry))) {
path_to_nameidata(path, nd);
err = -ENOENT;
}
}
b) in walk_component() and do_last():finish_lookup move the d_is_negative()
checks a bit up - into the body of preceding if () in the former and just
prior to the finish_lookup: in the latter.
AFAICS, the rest of d_is_negative() in fs/namei.c doesn't suffer that kind
of problem...
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