On Fri, May 22, 2009 6:36 pm, Andre Noll wrote:
> On 13:48, SandeepKsinha wrote:
>> Signed-off-by: Sandeep K Sinha <sandeepksinha@xxxxxxxxx>
>> Date: Fri May 22 13:46:56 2009 +0530
>>
>> Protecting mddev with barriers to avoid races.
>>
>> diff --git a/drivers/md/linear.c b/drivers/md/linear.c
>> index 9ad6ec4..e2dbda8 100644
>> --- a/drivers/md/linear.c
>> +++ b/drivers/md/linear.c
>> @@ -28,10 +28,12 @@
>> static inline dev_info_t *which_dev(mddev_t *mddev, sector_t sector)
>> {
>> int lo, mid, hi;
>> - linear_conf_t *conf = mddev_to_conf(mddev);
>> + linear_conf_t *conf;
>>
>> lo = 0;
>> hi = mddev->raid_disks - 1;
>> + barrier();
>> + conf = mddev_to_conf(mddev);
>
> Are you sure that a compiler barrier is sufficient here? Maybe we
> need smp_mb(), but I'm not familar with all the different memory
> barrier types that exist in the kernel.
I think we just want a read barrier here:
smb_rmb();
because it is a barrier between reading mddev->raid_disk and
reading mddev->private.
In linear_add, we want a write barrier
smb_wmb();
before setting mdev->raid_disks, and I think we also want one
before setting mddev->private to make sure that all the assignments
to newconf->whatever are stable.
NeilBrown
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