4.18-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
commit b59167ac7bafd804c91e49ad53c6d33a7394d4c8 upstream.
Eric reported that a sequence count loop using this_cpu_read() got optimized out. This is wrong, this_cpu_read() must imply READ_ONCE() because the interface is IRQ-safe, therefore an interrupt can have changed the per-cpu value.
Fixes: 7c3576d261ce ("[PATCH] i386: Convert PDA into the percpu section") Reported-by: Eric Dumazet edumazet@google.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Acked-by: Eric Dumazet edumazet@google.com Cc: hpa@zytor.com Cc: eric.dumazet@gmail.com Cc: bp@alien8.de Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20181011104019.748208519@infradead.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/include/asm/percpu.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- a/arch/x86/include/asm/percpu.h +++ b/arch/x86/include/asm/percpu.h @@ -185,22 +185,22 @@ do { \ typeof(var) pfo_ret__; \ switch (sizeof(var)) { \ case 1: \ - asm(op "b "__percpu_arg(1)",%0" \ + asm volatile(op "b "__percpu_arg(1)",%0"\ : "=q" (pfo_ret__) \ : "m" (var)); \ break; \ case 2: \ - asm(op "w "__percpu_arg(1)",%0" \ + asm volatile(op "w "__percpu_arg(1)",%0"\ : "=r" (pfo_ret__) \ : "m" (var)); \ break; \ case 4: \ - asm(op "l "__percpu_arg(1)",%0" \ + asm volatile(op "l "__percpu_arg(1)",%0"\ : "=r" (pfo_ret__) \ : "m" (var)); \ break; \ case 8: \ - asm(op "q "__percpu_arg(1)",%0" \ + asm volatile(op "q "__percpu_arg(1)",%0"\ : "=r" (pfo_ret__) \ : "m" (var)); \ break; \