Re: [PATCH v2] MIPS: vdso: flush the vdso data page to update it on all processes

Zubair Lutfullah Kakakhel
2016-03-30T15:22:12Z

Hi Hauke,

Could you share details of what version of glibc/rfs setup you are using?

Thanks.

Regards,
ZubairLK

On 29/03/16 22:36, Hauke Mehrtens wrote:
> On 02/21/2016 06:08 PM, Hauke Mehrtens wrote:
>> Without flushing the vdso data page the vdso call is working on dated
>> or unsynced data. This resulted in problems where the clock_gettime
>> vdso call returned a time 6 seconds later after a 3 seconds sleep,
>> while the syscall reported a time 3 sounds later, like expected. This
>> happened very often and I got these ping results for example:
>>
>> root@OpenWrt:/# ping 192.168.1.255
>> PING 192.168.1.255 (192.168.1.255): 56 data bytes
>> 64 bytes from 192.168.1.3: seq=0 ttl=64 time=0.688 ms
>> 64 bytes from 192.168.1.3: seq=1 ttl=64 time=4294172.045 ms
>> 64 bytes from 192.168.1.3: seq=2 ttl=64 time=4293968.105 ms
>> 64 bytes from 192.168.1.3: seq=3 ttl=64 time=4294055.920 ms
>> 64 bytes from 192.168.1.3: seq=4 ttl=64 time=4294671.913 ms
>>
>> This was tested on a Lantiq/Intel VRX288 (MIPS BE 34Kc V5.6 CPU with
>> two VPEs)
>>
>> Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
>> Cc: <stable@vger.kernel.org> # v4.4+
>
> This patch flushes the complete dcache of the CPU if cpu_has_dc_aliases
> is set.
>
> Calling flush_dcache_page(virt_to_page(&vdso_data)); improved the
> situation a litte bit but did not fix my problem.
>
> Could someone from Imagination please look into this problem. The page
> is linked into many virtual address spaces and when it gets modified by
> the kernel the user space processes are still accessing partly old data,
> even when lush_dcache_page() was called.
>
>> ---
>> arch/mips/kernel/vdso.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
>> index 975e997..8b0d974 100644
>> --- a/arch/mips/kernel/vdso.c
>> +++ b/arch/mips/kernel/vdso.c
>> @@ -20,6 +20,8 @@
>> #include <linux/timekeeper_internal.h>
>>
>> #include <asm/abi.h>
>> +#include <asm/cacheflush.h>
>> +#include <asm/page.h>
>> #include <asm/vdso.h>
>>
>> /* Kernel-provided data used by the VDSO. */
>> @@ -85,6 +87,8 @@ void update_vsyscall(struct timekeeper *tk)
>> }
>>
>> vdso_data_write_end(&vdso_data);
>> + flush_cache_vmap((unsigned long)&vdso_data,
>> + (unsigned long)&vdso_data + sizeof(vdso_data));
>> }
>>
>> void update_vsyscall_tz(void)
>> @@ -93,6 +97,8 @@ void update_vsyscall_tz(void)
>> vdso_data.tz_minuteswest = sys_tz.tz_minuteswest;
>> vdso_data.tz_dsttime = sys_tz.tz_dsttime;
>> }
>> + flush_cache_vmap((unsigned long)&vdso_data,
>> + (unsigned long)&vdso_data + sizeof(vdso_data));
>> }
>>
>> int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
>>
>
>