From 5db9fa9593e2ff69f2b95f9d59229dc4faaa564d Mon Sep 17 00:00:00 2001 From: Nathan Lynch Date: Tue, 22 Aug 2006 20:36:05 -0500 Subject: [POWERPC] Fix gettimeofday inaccuracies There are two problems in the powerpc gettimeofday code which can cause incorrect results to be returned. The first is that there is a race between do_gettimeofday and the timer interrupt: 1. do_gettimeofday does get_tb() 2. decrementer exception on boot cpu which runs timer_recalc_offset, which also samples the timebase and updates the do_gtod structure with a greater timebase value. 3. do_gettimeofday calls __do_gettimeofday, which leads to the negative result from tb_val - temp_varp->tb_orig_stamp. The second is caused by taking the boot cpu offline, which can cause the value of tb_last_jiffy to be increased past the currently available timebase, causing the same underflow as above. [paulus@samba.org - define and use data_barrier() instead of mb().] Signed-off-by: Nathan Lynch Signed-off-by: Paul Mackerras --- include/asm-powerpc/system.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'include/asm-powerpc') diff --git a/include/asm-powerpc/system.h b/include/asm-powerpc/system.h index 7307aa77567..4c9f5229e83 100644 --- a/include/asm-powerpc/system.h +++ b/include/asm-powerpc/system.h @@ -53,6 +53,15 @@ #define smp_read_barrier_depends() do { } while(0) #endif /* CONFIG_SMP */ +/* + * This is a barrier which prevents following instructions from being + * started until the value of the argument x is known. For example, if + * x is a variable loaded from memory, this prevents following + * instructions from being executed until the load has been performed. + */ +#define data_barrier(x) \ + asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory"); + struct task_struct; struct pt_regs; -- cgit v1.2.3-70-g09d2