Messages in this thread | | | From | (Eric W. Biederman) | Date | Thu, 20 Feb 2020 17:37:44 -0600 | Subject | Re: [PATCH 0/7] proc: Dentry flushing without proc_mnt |
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Al Viro <viro@zeniv.linux.org.uk> writes:
> On Thu, Feb 20, 2020 at 03:02:22PM -0800, Linus Torvalds wrote: >> On Thu, Feb 20, 2020 at 12:48 PM Eric W. Biederman >> <ebiederm@xmission.com> wrote: >> > >> > Linus, does this approach look like something you can stand? >> >> A couple of worries, although one of them seem to have already been >> resolved by Al. >> >> I think the real gatekeeper should be Al in general. But other than >> the small comments I had, I think this might work just fine. >> >> Al? > > I'll need to finish RTFS there; I have initially misread that patch, > actually - Eric _is_ using that thing both for those directories > and for sysctl inodes. And the prototype for that machinery (the > one he'd pulled from proc_sysctl.c) is playing with pinning superblocks > way too much; for per-pid directories that's not an issue, but > for sysctl table removal you are very likely to hit a bunch of > evictees on the same superblock...
I saw that was possible. If the broad strokes look correct I don't have a problem at all with optimizing for the case where many of the entries are for inodes on the same superblock. I just had enough other details on my mind I was afraid if I got a little more clever I would have introduced a typo somewhere.
I wish I could limit the sysctl parts to just directories, but unfortunately the sysctl tables don't always give a guarantee that a directory is what will be removed. But sysctls do have one name per inode invarant like fat. There is no way to express a sysctl table that doesn't have that invariant.
As for d_find_alias/d_invalidate.
Just for completeness I wanted to write a loop:
while (dentry = d_find_alias(inode)) { d_invalidate(dentry); dput(dentry); }
Unfortunately that breaks on directories, because for directories d_find_alias turns into d_find_any_alias, and continues to return aliases even when they are unhashed.
It might be nice to write a cousin of d_prune_aliases call it d_invalidate_aliases that just does that loop the correct way in dcache.c
Eric
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