* [PATCH 4.4 01/46] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts [not found] <20171019134845.293630834@linuxfoundation.org> @ 2017-10-19 13:48 ` Greg Kroah-Hartman 2017-10-19 13:48 ` Greg Kroah-Hartman 0 siblings, 1 reply; 2+ messages in thread From: Greg Kroah-Hartman @ 2017-10-19 13:48 UTC (permalink / raw) To: linux-kernel Cc: Greg Kroah-Hartman, stable, Mark Rutland, Arnd Bergmann, Christoph Lameter, Peter Zijlstra, Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch 4.4-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> [Mark: backport to v4.4.y] Signed-off-by: Mark Rutland <mark.rutland@arm.com> 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 @@ -105,15 +105,35 @@ do { \ (__ret); \ }) -#define this_cpu_generic_read(pcp) \ +#define __this_cpu_generic_read_nopreempt(pcp) \ ({ \ typeof(pcp) __ret; \ preempt_disable(); \ - __ret = *this_cpu_ptr(&(pcp)); \ + __ret = READ_ONCE(*raw_cpu_ptr(&(pcp))); \ preempt_enable(); \ __ret; \ }) +#define __this_cpu_generic_read_noirq(pcp) \ +({ \ + typeof(pcp) __ret; \ + unsigned long __flags; \ + raw_local_irq_save(__flags); \ + __ret = *raw_cpu_ptr(&(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; \ ^ permalink raw reply [flat|nested] 2+ messages in thread
* [PATCH 4.4 01/46] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts 2017-10-19 13:48 ` [PATCH 4.4 01/46] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts Greg Kroah-Hartman @ 2017-10-19 13:48 ` Greg Kroah-Hartman 0 siblings, 0 replies; 2+ messages in thread From: Greg Kroah-Hartman @ 2017-10-19 13:48 UTC (permalink / raw) To: linux-kernel Cc: Greg Kroah-Hartman, stable, Mark Rutland, Arnd Bergmann, Christoph Lameter, Peter Zijlstra, Pranith Kumar, Tejun Heo, Thomas Gleixner, linux-arch 4.4-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> [Mark: backport to v4.4.y] Signed-off-by: Mark Rutland <mark.rutland@arm.com> 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 @@ -105,15 +105,35 @@ do { \ (__ret); \ }) -#define this_cpu_generic_read(pcp) \ +#define __this_cpu_generic_read_nopreempt(pcp) \ ({ \ typeof(pcp) __ret; \ preempt_disable(); \ - __ret = *this_cpu_ptr(&(pcp)); \ + __ret = READ_ONCE(*raw_cpu_ptr(&(pcp))); \ preempt_enable(); \ __ret; \ }) +#define __this_cpu_generic_read_noirq(pcp) \ +({ \ + typeof(pcp) __ret; \ + unsigned long __flags; \ + raw_local_irq_save(__flags); \ + __ret = *raw_cpu_ptr(&(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; \ ^ permalink raw reply [flat|nested] 2+ messages in thread
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2017-10-19 13:48 ` [PATCH 4.4 01/46] percpu: make this_cpu_generic_read() atomic w.r.t. interrupts Greg Kroah-Hartman
2017-10-19 13:48 ` Greg Kroah-Hartman
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