Sorry to take so long to get back to this Jeff.
On Wed, 20 Apr 2005, Jeff Moyer wrote:
==> Regarding Re: [PATCH 1/3] autofs4 - expiring filesystem from under process;
[EMAIL PROTECTED] adds:
raven> On Mon, 11 Apr 2005, Jeff Moyer wrote:
==> Regarding [PATCH 1/3] autofs4 - expiring filesystem from under
process; [EMAIL PROTECTED] adds:
Could also please explain how the following is handled:
expire process runs and issues AUTOFS_EXPIRE_MULTI, which sets
AUTOFS_INF_EXPIRING in flags. While the expire is in progress, another
process access the directory in question, causing a call to
try_to_fill_dentry. try_to_fill_dentry sees the AUTOFS_INF_EXPIRING
flag is set, and so calls autofs4_wait with notify set to NFY_NONE.
However, when we take the wq sem, we find that the expire has finished,
and thus create a new wq entry. Because NFY_NONE is set, we don't tell
the daemon.
So how will this process ever get woken up?
raven> I've thought about this for quite a while and I think all that's
raven> needed is to recognise that we're about to expire a dentry that's
raven> not mounted anymore.
raven> Can you think of a case for which this patch fails?
I don't see how the patch you provided addresses the race between an expire
event and a lookup. The real issue here is that the checking of
AUTOFS_INF_EXPIRING and the list operations associated therewith need to
happen atomically. Until this happens, we will have races.
I don't think that's quite how this process works.
In this case, since the the directory exists, we always come to
autofs4_wait via autofs4_revalidate and only during an expire. If the
expire finishes and we attempt to create a new wait as you describe then
all that needs to be done is to return a fail instead of waiting and rely
on the subsequent autofs4_lookup call to perform the requested mount.
For the normal case, when the process waits and then returns at expire
completion has the same semantics. So for a NFY_NONE wait request,
checking if the dentry is a mountpoint and returning -ENOENT is sufficient
(in fact the return code itself is not significant). Please check
do_lookup in namei.c and I think you will see what I mean.
Ian
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