Re: [PATCH v3 -next 1/1] module: kallsyms: Ensure preemption in add_kallsyms() with PREEMPT_RT
From: Luis Chamberlain <mcgrof@kernel.org>
Date: 2022-07-11 17:32:54
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On Mon, Jul 11, 2022 at 06:17:19PM +0100, Aaron Tomlin wrote:
The commit 08126db5ff73 ("module: kallsyms: Fix suspicious rcu usage")
under PREEMPT_RT=y, disabling preemption introduced an unbounded
latency since the loop is not fixed. This change caused a regression
since previously preemption was not disabled and we would dereference
RCU-protected pointers explicitly. That being said, these pointers
cannot change.
Before kallsyms-specific data is prepared/or set-up, we ensure that
the unformed module is known to be unique i.e. does not already exist
(see load_module()). Therefore, we can fix this by using the common and
more appropriate RCU flavour as this section of code can be safely
preempted.
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Fixes: 08126db5ff73 ("module: kallsyms: Fix suspicious rcu usage")
Signed-off-by: Aaron Tomlin <redacted>Thanks! Queued up! Luis