linux-kernel - Re: [linus:master] [eventfs] 852e46e239: BUG:unable_to_handle_page_fault_for

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Date: Mon, 29 Jan 2024 19:35:49 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
 lkp@...el.com, linux-kernel@...r.kernel.org, Masami Hiramatsu
 <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, Christian Brauner
 <brauner@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Ajay Kaher
 <ajay.kaher@...adcom.com>, linux-trace-kernel@...r.kernel.org
Subject: Re: [linus:master] [eventfs] 852e46e239:
 BUG:unable_to_handle_page_fault_for_address

On Mon, 29 Jan 2024 16:01:25 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> I'll go see what's up with the "create it again" case - I don't
> immediately see what's wrong.

Interesting. I added a printk in the lookup, and just did this:

 # cd /sys/kernel/tracing
 # ls events/kprobes

And it showed that it tried to see if "kprobes" existed in the lookup.
Which it did not because I haven't created any kprobes yet.

Then I did:

 # echo 'p:sched schedule' >> /sys/kernel/tracing/kprobe_events
 # ls -l events/kprobes/
ls: cannot access 'events/kprobes/': No such file or directory

Where it should now exist but doesn't. But the lookup code never triggered.

If the lookup fails, does it cache the result?

-- Steve