From 20fb6c997600012209699564a79911584dd5876b Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 9 Dec 2022 13:41:44 -0500 Subject: [PATCH] x86/mm/kmmio: Use rcu_read_lock_sched_notrace() The mmiotrace tracer is "special". The purpose is to help reverse engineer binary drivers by removing the memory allocated by the driver and when the driver goes to access it, a fault occurs, the mmiotracer will record what the driver was doing and then do the work on its behalf by single stepping through the process. But to achieve this ability, it must do some special things. One is to take the rcu_read_lock() when the fault occurs, and then release it in the breakpoint that is single stepping. This makes lockdep unhappy, as it changes the state of RCU from within an exception that is not contained in that exception, and we get a nasty splat from lockdep. Instead, switch to rcu_read_lock_sched_notrace() as the RCU sched variant has the same grace period as normal RCU. This is basically the same as rcu_read_lock() but does not make lockdep complain about it. Note, the preempt_disable() is still needed as it uses preempt_enable_no_resched(). Link: https://lore.kernel.org/linux-trace-kernel/20221209134144.04f33626@gandalf.local.home Cc: Masami Hiramatsu Cc: Andrew Morton Cc: Karol Herbst Cc: Pekka Paalanen Cc: Dave Hansen Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Acked-by: Paul E. McKenney Signed-off-by: Steven Rostedt (Google) --- arch/x86/mm/kmmio.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c index edb4864501582..853c49877c161 100644 --- a/arch/x86/mm/kmmio.c +++ b/arch/x86/mm/kmmio.c @@ -254,7 +254,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr) * again. */ preempt_disable(); - rcu_read_lock(); + rcu_read_lock_sched_notrace(); faultpage = get_kmmio_fault_page(page_base); if (!faultpage) { @@ -323,7 +323,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr) return 1; /* fault handled */ no_kmmio: - rcu_read_unlock(); + rcu_read_unlock_sched_notrace(); preempt_enable_no_resched(); return ret; } @@ -363,7 +363,7 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs) /* These were acquired in kmmio_handler(). */ ctx->active--; BUG_ON(ctx->active); - rcu_read_unlock(); + rcu_read_unlock_sched_notrace(); preempt_enable_no_resched(); /* -- 2.30.2