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    Subject[PATCH 4.13 112/160] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts
    Date
    4.13-stable review patch.  If anyone has any objections, please let me know.

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

    From: Mark Rutland <mark.rutland@arm.com>

    commit e88d62cd4b2f0b1ae55e9008e79c2794b1fc914d upstream.

    As raw_cpu_generic_read() is a plain read from a raw_cpu_ptr() address,
    it's possible (albeit unlikely) that the compiler will split the access
    across multiple instructions.

    In this_cpu_generic_read() we disable preemption but not interrupts
    before calling raw_cpu_generic_read(). Thus, an interrupt could be taken
    in the middle of the split load instructions. If a this_cpu_write() or
    RMW this_cpu_*() op is made to the same variable in the interrupt
    handling path, this_cpu_read() will return a torn value.

    For native word types, we can avoid tearing using READ_ONCE(), but this
    won't work in all cases (e.g. 64-bit types on most 32-bit platforms).
    This patch reworks this_cpu_generic_read() to use READ_ONCE() where
    possible, otherwise falling back to disabling interrupts.

    Signed-off-by: Mark Rutland <mark.rutland@arm.com>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Pranith Kumar <bobby.prani@gmail.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-arch@vger.kernel.org
    Signed-off-by: Tejun Heo <tj@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    include/asm-generic/percpu.h | 24 ++++++++++++++++++++++--
    1 file changed, 22 insertions(+), 2 deletions(-)

    --- a/include/asm-generic/percpu.h
    +++ b/include/asm-generic/percpu.h
    @@ -115,15 +115,35 @@ do { \
    (__ret); \
    })

    -#define this_cpu_generic_read(pcp) \
    +#define __this_cpu_generic_read_nopreempt(pcp) \
    ({ \
    typeof(pcp) __ret; \
    preempt_disable_notrace(); \
    - __ret = raw_cpu_generic_read(pcp); \
    + __ret = READ_ONCE(*raw_cpu_ptr(&(pcp))); \
    preempt_enable_notrace(); \
    __ret; \
    })

    +#define __this_cpu_generic_read_noirq(pcp) \
    +({ \
    + typeof(pcp) __ret; \
    + unsigned long __flags; \
    + raw_local_irq_save(__flags); \
    + __ret = raw_cpu_generic_read(pcp); \
    + raw_local_irq_restore(__flags); \
    + __ret; \
    +})
    +
    +#define this_cpu_generic_read(pcp) \
    +({ \
    + typeof(pcp) __ret; \
    + if (__native_word(pcp)) \
    + __ret = __this_cpu_generic_read_nopreempt(pcp); \
    + else \
    + __ret = __this_cpu_generic_read_noirq(pcp); \
    + __ret; \
    +})
    +
    #define this_cpu_generic_to_op(pcp, val, op) \
    do { \
    unsigned long __flags; \

    \
     
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      Last update: 2017-10-10 22:19    [W:5.385 / U:0.012 seconds]
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