diff options
author | Nathan Lynch <ntl@pobox.com> | 2006-08-22 20:36:05 -0500 |
---|---|---|
committer | Paul Mackerras <paulus@samba.org> | 2006-08-23 15:51:18 +1000 |
commit | 5db9fa9593e2ff69f2b95f9d59229dc4faaa564d (patch) | |
tree | d58ba58c05408edf8993d0da5a31b3ea3df1a053 /include/asm-powerpc/system.h | |
parent | aa74a30be971c632d734e487df42278b1cf85151 (diff) |
[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 <ntl@pobox.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Diffstat (limited to 'include/asm-powerpc/system.h')
-rw-r--r-- | include/asm-powerpc/system.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/include/asm-powerpc/system.h b/include/asm-powerpc/system.h index 7307aa775671..4c9f5229e833 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; |