From: Al Viro <viro@zeniv.linux.org.uk>
To: Max Kellermann <max.kellermann@ionos.com>
Cc: linux-fsdevel@vger.kernel.org,
Christian Brauner <brauner@kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 20/21] __dentry_kill(): new locking scheme
Date: Mon, 7 Jul 2025 20:31:15 +0100 [thread overview]
Message-ID: <20250707193115.GH1880847@ZenIV> (raw)
In-Reply-To: <CAKPOu+-QzSzUw4q18FsZFR74OJp90rs9X08gDxWnsphfwfwxoQ@mail.gmail.com>
On Mon, Jul 07, 2025 at 08:11:43PM +0200, Max Kellermann wrote:
> On Mon, Jul 7, 2025 at 8:00 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> > Well, it tries to evict all non-busy dentries, along with the ones that
> > are only busy due to (non-busy) children, etc.
>
> But why did you add code that keeps looping if a dead/killed dentry
> was found, even though there is no code to do anything with such a
> dentry?
Huh? That dentry contributes a soon-to-be-gone reference to parent;
it's still there in the tree, but it's already in process of being
evicted. The parent will remain busy the end of __dentry_kill().
It is *not* dead; if you want slightly distrubing metaphors, it is already
beyond resuscitation (that's what the negative refcount indicates), but
it has not finished dying yet. DCACHE_DENTRY_KILLED in flags ==
"it's dead", and those can't be found in the tree/hash/list of aliases/etc.
Negative refcount on something found in the tree == "it's busy dying at
the moment" and parent is kept busy until that's over.
And we *want* those to be findable in the tree - think e.g. of umount.
We really don't want to progress to destroying fs-private data structures
before all dentries are disconnected from inodes, etc.
next prev parent reply other threads:[~2025-07-07 19:31 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-24 6:02 [RFC][PATCHSET v3] simplifying fast_dput(), dentry_kill() et.al Al Viro
2023-11-24 6:04 ` [PATCH v3 01/21] switch nfsd_client_rmdir() to use of simple_recursive_removal() Al Viro
2023-11-24 6:04 ` [PATCH v3 02/21] coda_flag_children(): cope with dentries turning negative Al Viro
2023-11-24 21:22 ` Linus Torvalds
2023-11-24 22:58 ` Paul E. McKenney
2023-11-24 6:04 ` [PATCH v3 03/21] dentry: switch the lists of children to hlist Al Viro
2023-11-24 7:44 ` Amir Goldstein
2023-11-24 7:55 ` Al Viro
2023-11-24 8:02 ` Amir Goldstein
2023-11-24 6:04 ` [PATCH v3 04/21] centralize killing dentry from shrink list Al Viro
2023-11-24 6:04 ` [PATCH v3 05/21] shrink_dentry_list(): no need to check that dentry refcount is marked dead Al Viro
2023-11-24 6:04 ` [PATCH v3 06/21] fast_dput(): having ->d_delete() is not reason to delay refcount decrement Al Viro
2023-11-24 6:04 ` [PATCH v3 07/21] fast_dput(): handle underflows gracefully Al Viro
2023-11-24 6:04 ` [PATCH v3 08/21] fast_dput(): new rules for refcount Al Viro
2023-11-24 6:04 ` [PATCH v3 09/21] __dput_to_list(): do decrement of refcount in the callers Al Viro
2023-11-24 6:04 ` [PATCH v3 10/21] make retain_dentry() neutral with respect to refcounting Al Viro
2023-11-24 6:04 ` [PATCH v3 11/21] __dentry_kill(): get consistent rules for victim's refcount Al Viro
2023-11-24 6:04 ` [PATCH v3 12/21] dentry_kill(): don't bother with retain_dentry() on slow path Al Viro
2023-11-24 6:04 ` [PATCH v3 13/21] Call retain_dentry() with refcount 0 Al Viro
2023-11-24 6:04 ` [PATCH v3 14/21] fold the call of retain_dentry() into fast_dput() Al Viro
2023-11-24 6:04 ` [PATCH v3 15/21] don't try to cut corners in shrink_lock_dentry() Al Viro
2023-11-24 6:04 ` [PATCH v3 16/21] fold dentry_kill() into dput() Al Viro
2023-11-24 6:04 ` [PATCH v3 17/21] to_shrink_list(): call only if refcount is 0 Al Viro
2023-11-24 6:04 ` [PATCH v3 18/21] switch select_collect{,2}() to use of to_shrink_list() Al Viro
2023-11-24 6:04 ` [PATCH v3 19/21] d_prune_aliases(): use a shrink list Al Viro
2023-11-24 6:04 ` [PATCH v3 20/21] __dentry_kill(): new locking scheme Al Viro
2025-07-07 17:20 ` Max Kellermann
2025-07-07 17:29 ` Al Viro
2025-07-07 17:43 ` Max Kellermann
2025-07-07 18:00 ` Al Viro
2025-07-07 18:11 ` Max Kellermann
2025-07-07 19:31 ` Al Viro [this message]
2025-07-07 20:00 ` Max Kellermann
2025-07-07 20:31 ` Al Viro
2025-07-07 20:39 ` Max Kellermann
2025-07-07 20:49 ` Al Viro
2025-07-07 20:52 ` Max Kellermann
2025-07-07 20:59 ` Al Viro
2025-07-07 21:06 ` Max Kellermann
2025-07-07 21:32 ` Al Viro
2025-07-07 21:47 ` Max Kellermann
2025-07-07 22:19 ` Al Viro
2025-07-07 22:37 ` Al Viro
2025-07-08 4:45 ` Max Kellermann
2025-07-07 22:26 ` Al Viro
2023-11-24 6:04 ` [PATCH v3 21/21] retain_dentry(): introduce a trimmed-down lockless variant Al Viro
2023-11-24 21:28 ` [RFC][PATCHSET v3] simplifying fast_dput(), dentry_kill() et.al Linus Torvalds
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20250707193115.GH1880847@ZenIV \
--to=viro@zeniv.linux.org.uk \
--cc=brauner@kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=max.kellermann@ionos.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).