The per-cpu preempt count of x86 contains two values, the actual preempt count and the inverted PREEMPT_NEED_RESCHED bit. If a corrupted preempt count is detected the preempt_count_set function is used to reset the preempt count.
In case the inverted PREEMPT_NEED_RESCHED bit is zero at the time of the reset, the preemption indication is lost. Use raw_cpu_cmpxchg_4 to reset only the count part and leave the PREEMPT_NEED_RESCHED bit as it is. Signed-off-by: Martin Schwidefsky <[email protected]> --- arch/x86/include/asm/preempt.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index 17f2186..ec1f3c6 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -24,7 +24,13 @@ static __always_inline int preempt_count(void) static __always_inline void preempt_count_set(int pc) { - raw_cpu_write_4(__preempt_count, pc); + int old, new; + + do { + old = raw_cpu_read_4(__preempt_count); + new = (old & PREEMPT_NEED_RESCHED) | + (pc & ~PREEMPT_NEED_RESCHED); + } while (raw_cpu_cmpxchg_4(__preempt_count, old, new) != old); } /* -- 1.9.1
