From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: kernel test robot <oliver.sang@intel.com>,
oe-lkp@lists.linux.dev, lkp@intel.com,
linux-kernel@vger.kernel.org,
Masami Hiramatsu <mhiramat@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Christian Brauner <brauner@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Ajay Kaher <ajay.kaher@broadcom.com>,
linux-trace-kernel@vger.kernel.org
Subject: Re: [linus:master] [eventfs] 852e46e239: BUG:unable_to_handle_page_fault_for_address
Date: Mon, 29 Jan 2024 14:35:37 -0800 [thread overview]
Message-ID: <CAHk-=wjV6+U1FQ8wzQ5ASmqGgby+GZ6wpdh0NrJgA43mc+TEwA@mail.gmail.com> (raw)
In-Reply-To: <20240129172200.1725f01b@gandalf.local.home>
On Mon, 29 Jan 2024 at 14:21, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> But crashes with just a:
>
> # ls /sys/kernel/tracing/events
>
> [ 66.423983] ------------[ cut here ]------------
> [ 66.426447] kernel BUG at fs/dcache.c:1876!
Duh.
That's a bit too much copy-and-paste by me.
So what is going on is that a ->lookup() function should *not* call
d_instantiate() at all, and the only reason it actually used to work
here was due to the incorrect "simple_lookup()", which basically did
all the preliminaries.
A ->lookup() should do 'd_add()' on the dentry.
So just replace all the d_instantiate() calls there with "d_add()"
instead. I think that will fix it.
Basically the "simple_lookup()" had done the "d_add(dentry, NULL)",
and at that point the "d_instantiate()" just exposed the inode and
turned the negative dentry into a positive one.
So "d_add()" is "I'm adding the inode to a new dentry under lookup".
And "d_instantiate()" is "I'm adding this inode to an existing dentry
that used to be negative"
And so the old "d_add(NULL)+d_instantiate(inode)" _kind_ of worked,
except it made that negative dentry visible for a short while.
And when I did the cleanup, I didn't think of this thing, so I left
the d_instantiate() calls as such, even though they now really need to
be d_add().
Hope that explains it.
And I hope there aren't any other stupid things I missed like that.
Linus
next prev parent reply other threads:[~2024-01-29 22:35 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-29 2:58 [linus:master] [eventfs] 852e46e239: BUG:unable_to_handle_page_fault_for_address kernel test robot
2024-01-29 4:36 ` Linus Torvalds
2024-01-29 17:01 ` Steven Rostedt
2024-01-29 17:40 ` Linus Torvalds
2024-01-29 17:44 ` Steven Rostedt
2024-01-29 17:45 ` Steven Rostedt
2024-01-29 17:56 ` Linus Torvalds
2024-01-29 17:55 ` Linus Torvalds
2024-01-29 19:24 ` Linus Torvalds
2024-01-29 19:51 ` Linus Torvalds
2024-01-29 20:26 ` Steven Rostedt
2024-01-29 20:51 ` Linus Torvalds
2024-01-29 21:45 ` Steven Rostedt
2024-01-29 22:19 ` Linus Torvalds
2024-01-29 21:55 ` Steven Rostedt
2024-01-29 22:22 ` Steven Rostedt
2024-01-29 22:35 ` Linus Torvalds [this message]
2024-01-29 22:42 ` Linus Torvalds
2024-01-29 22:49 ` Steven Rostedt
2024-01-30 0:01 ` Linus Torvalds
2024-01-30 0:35 ` Steven Rostedt
2024-01-30 1:50 ` Linus Torvalds
2024-01-30 3:56 ` Linus Torvalds
2024-01-30 8:43 ` Linus Torvalds
2024-01-30 9:12 ` Linus Torvalds
2024-01-30 12:45 ` Rasmus Villemoes
2024-01-30 14:39 ` Steven Rostedt
2024-01-30 16:49 ` Steven Rostedt
2024-01-30 16:55 ` Linus Torvalds
2024-01-30 17:06 ` Steven Rostedt
2024-01-30 17:09 ` Linus Torvalds
2024-01-30 16:51 ` Linus Torvalds
2024-01-30 18:23 ` Steven Rostedt
2024-01-30 19:19 ` Linus Torvalds
2024-01-30 19:37 ` Steven Rostedt
2024-01-30 19:54 ` Linus Torvalds
2024-01-30 20:04 ` Steven Rostedt
2024-01-31 15:58 ` Steven Rostedt
2024-01-31 16:13 ` Steven Rostedt
2024-01-31 17:28 ` Steven Rostedt
2024-01-31 17:26 ` Steven Rostedt
2024-01-31 19:35 ` Linus Torvalds
2024-01-31 19:42 ` Steven Rostedt
2024-01-30 18:36 ` Steven Rostedt
2024-01-29 22:47 ` Steven Rostedt
2024-01-29 23:15 ` Steven Rostedt
2024-01-30 2:08 ` Al Viro
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