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    SubjectRe: [PATCH v2 1/1] context_tracking: Use arch_atomic_read() in __ct_state for KASAN
    Apologies, I accidentally picked this specific commit up in my recent
    git format-patch which ended up sending it out. Totally unintended.

    On Wed, Jun 22, 2022 at 6:51 PM Joel Fernandes (Google)
    <joel@joelfernandes.org> wrote:
    >
    > From: "Paul E. McKenney" <paulmck@kernel.org>
    >
    > 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@kernel.org>
    > Cc: Frederic Weisbecker <frederic@kernel.org>
    > Cc: Marco Elver <elver@google.com>
    > Reviewed-by: Marco Elver <elver@google.com>
    > ---
    > include/linux/context_tracking_state.h | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
    > index 0aecc07fb4f5..81c51e5f0314 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
    >
    > --
    > 2.37.0.rc0.104.g0611611a94-goog
    >

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