From: Steven Rostedt <rostedt@goodmis.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux Trace Devel <linux-trace-devel@vger.kernel.org>,
Christian Brauner <brauner@kernel.org>,
Ajay Kaher <ajay.kaher@broadcom.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] eventfs: Have inodes have unique inode numbers
Date: Sun, 28 Jan 2024 16:19:35 -0500 [thread overview]
Message-ID: <20240128161935.417d36b3@rorschach.local.home> (raw)
In-Reply-To: <CAHk-=whKJ6dzQJX27gvL4Xug5bFRKW7_Cx4XpngMKmWxOtb+Qg@mail.gmail.com>
On Sun, 28 Jan 2024 12:53:31 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:
> Honestly, you should just *always* do refcounting. No "free after RCU
> delay" as an alternative. Just refcount it.
>
> Now, the RCU delay may be needed if the lookup of said structure
> happens under RCU, but no, saying "I use SRCU to make sure the
> lifetime is at least X" is just broken.
>
> The refcount is what gives the lifetime. Any form of RCU-delaying
> should then be purely about non-refcounting RCU lookups that may
> happen as the thing is dying (and said lookup should *look* at the
> refcount and say "oh, this is dead, I'm not returning this".
The deleting of the ei is done outside the VFS logic. I use SRCU to
synchronize looking at the ei children in the lookup. On deletion, I
grab the eventfs_mutex, set ei->is_freed and then wait for SRCU to
finish before freeing.
The lookup checks ei->is_freed and doesn't do anything if set, but most
that logic is under the SRCU, which is what I want to make sure is
finished before the ei is deleted.
Hmm, I still need the logic for iput(), as dentry->d_fsdata can still
access the ei. That's where I need to have the ref counters. For a
lookup, I need to up the ref count when I create a new inode for the ei
or its children. Then in the iput() I decrement the ei ref count. I can
only free the ei if the ref count is zero.
The ref count is for knowing if an ei is referenced by a
dentry->d_fsdata, and the SRCU is to make sure there's no lookups
accessing an ei.
-- Steve
next prev parent reply other threads:[~2024-01-28 21:19 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-26 20:02 [PATCH] eventfs: Have inodes have unique inode numbers Steven Rostedt
2024-01-26 20:25 ` Linus Torvalds
2024-01-26 21:26 ` Steven Rostedt
2024-01-26 21:31 ` Linus Torvalds
2024-01-26 21:43 ` Steven Rostedt
2024-01-26 21:36 ` Linus Torvalds
2024-01-26 21:42 ` Steven Rostedt
2024-01-26 21:49 ` Linus Torvalds
2024-01-26 22:08 ` Steven Rostedt
2024-01-26 22:26 ` Linus Torvalds
2024-01-27 14:47 ` Steven Rostedt
2024-01-28 14:42 ` Steven Rostedt
2024-01-26 22:14 ` Mathieu Desnoyers
2024-01-26 22:29 ` Linus Torvalds
2024-01-26 22:41 ` Mathieu Desnoyers
2024-01-26 22:49 ` Linus Torvalds
2024-01-29 16:00 ` Mathieu Desnoyers
2024-01-29 18:58 ` Linus Torvalds
2024-01-26 22:34 ` Matthew Wilcox
2024-01-26 22:40 ` Mathieu Desnoyers
2024-01-26 22:48 ` Linus Torvalds
2024-01-26 23:04 ` Matthew Wilcox
2024-01-26 23:11 ` Linus Torvalds
2024-01-26 23:17 ` Linus Torvalds
2024-01-27 9:36 ` Andreas Schwab
2024-01-27 21:47 ` Linus Torvalds
2024-01-28 20:15 ` Steven Rostedt
2024-01-28 20:53 ` Linus Torvalds
2024-01-28 21:08 ` Linus Torvalds
2024-01-28 22:01 ` Steven Rostedt
2024-01-28 22:17 ` Linus Torvalds
2024-01-28 22:26 ` Steven Rostedt
2024-01-28 21:11 ` Steven Rostedt
2024-01-28 21:19 ` Steven Rostedt [this message]
2024-01-28 21:43 ` Linus Torvalds
2024-01-28 22:07 ` Linus Torvalds
2024-01-28 22:17 ` Steven Rostedt
2024-01-28 22:25 ` Linus Torvalds
2024-01-28 22:51 ` Steven Rostedt
2024-01-28 23:24 ` Linus Torvalds
2024-01-28 23:59 ` Steven Rostedt
2024-01-29 0:21 ` Steven Rostedt
2024-01-29 1:00 ` Linus Torvalds
2024-01-29 1:42 ` Linus Torvalds
2024-01-29 2:32 ` Steven Rostedt
2024-01-29 3:40 ` Steven Rostedt
2024-01-29 4:01 ` Linus Torvalds
2024-01-29 2:09 ` Steven Rostedt
2024-01-29 6:44 ` Amir Goldstein
2024-01-29 9:32 ` Steven Rostedt
2024-01-27 15:26 ` David Laight
2024-01-27 20:01 ` Linus Torvalds
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