linux-kernel - Re: [paulmck-rcu:pmladek.2022.06.15a] BUILD SUCCESS WITH WARNING 0ba7324b44282870af740a5a121add62c7f5f730

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Message-ID: <20220616200548.GT1790663@paulmck-ThinkPad-P17-Gen-1>
Date:   Thu, 16 Jun 2022 13:05:48 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     kernel test robot <lkp@...el.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [paulmck-rcu:pmladek.2022.06.15a] BUILD SUCCESS WITH WARNING
 0ba7324b44282870af740a5a121add62c7f5f730

On Fri, Jun 17, 2022 at 03:33:27AM +0800, kernel test robot wrote:
> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git pmladek.2022.06.15a
> branch HEAD: 0ba7324b44282870af740a5a121add62c7f5f730  printk: Wait for the global console lock when the system is going down
> 
> Warning reports:
> 
> https://lore.kernel.org/lkml/202206160411.v3iL3YC0-lkp@intel.com
> https://lore.kernel.org/llvm/202206160421.Gnl3tpxc-lkp@intel.com
> 
> Warning: (recently discovered and may have been fixed)
> 
> vmlinux.o: warning: objtool: __ct_user_enter+0x7f: call to __kasan_check_read() leaves .noinstr.text section
> vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section

Here is the alleged fix, and thank you for testing!

							Thanx, Paul

------------------------------------------------------------------------

commit 571252796c089880b804835f6cfc9c3da3ae8c4f
Author: Paul E. McKenney <paulmck@...nel.org>
Date:   Thu Jun 16 09:30:37 2022 -0700

    context_tracking: Use arch_atomic_read() in __ct_state for KASAN
    
    Context tracking's __ct_state() function can be invoked from noinstr state
    where RCU is not watching.  This means that its use of atomic_read()
    causes KASAN to invoke the non-noinstr __kasan_check_read() function
    from the noinstr function __ct_state().  This is problematic because
    someone tracing the __kasan_check_read() function could get a nasty
    surprise because of RCU not watching.
    
    This commit therefore replaces the __ct_state() function's use of
    atomic_read() with arch_atomic_read(), which KASAN does not attempt to
    add instrumention to.
    
    Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
    Cc: Frederic Weisbecker <frederic@...nel.org>
    Cc: Marco Elver <elver@...gle.com>
    Reviewed-by: Marco Elver <elver@...gle.com>

diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index 0aecc07fb4f50..81c51e5f03143 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -49,7 +49,7 @@ DECLARE_PER_CPU(struct context_tracking, context_tracking);
 
 static __always_inline int __ct_state(void)
 {
-	return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
+	return arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
 }
 #endif