hi, Borislav
thanks for your kind reply. :)
On 2015年07月22日 15:46, Borislav Petkov wrote:
> On Wed, Jul 22, 2015 at 01:38:48PM +0800, Pan Xinhui wrote:
>> From: Pan Xinhui <xinhuix....@intel.com>
>>
>> It's more reasonable to unlock memtype_lock right after
>> rbt_memtype_check_insert. memtype_lock protects all data stored in
>> rb-tree from multiple access. It's not cool to call kfree, pr_info, etc
>> with this lock held. So move spin_unlock a little ahead.
>>
>> If *new* succeed to be stored into the rb-tree, we might hit panic.
>> Because we access *new* in dprintk "cattr_name(new->type)". Data stored
>> in the rb-tree might be freed at any possbile time. It's abviously wrong
>> to access such data without lock held. As new->type might be changed in
>> rbt_memtype_check_insert, so save new->type to actual_type, then use
>> actual_type in dprintk.
>>
>> Signed-off-by: Pan Xinhui <xinhuix....@intel.com>
>> ---
>> change from v2:
>> update comments.
>> change from V1:
>> fix an access of *new* without memtype_lock held.
>> ---
>> arch/x86/mm/pat.c | 15 +++++++++------
>> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> This patch still doesn't update the comments over memtype_lock.
>
sorry for that.
how about:
memtype_lock protects the rb-tree root and the rb-nodes which is a field of
memtype from delete/add/lookup in a race.
>>
>> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
>> index 188e3e0..894a096 100644
>> --- a/arch/x86/mm/pat.c
>> +++ b/arch/x86/mm/pat.c
>> @@ -538,22 +538,25 @@ int reserve_memtype(u64 start, u64 end, enum
>> page_cache_mode req_type,
>> new->type = actual_type;
>>
>> spin_lock(&memtype_lock);
>> -
>> err = rbt_memtype_check_insert(new, new_type);
>> + /*
>> + * new->type might be changed in rbt_memtype_check_insert.
>> + * So save new->type to actual_type as dprintk uses it.
>> + * We are not allowed to touch new after unlocking memtype_lock.
>> + */
>> + actual_type = new->type;
>
> We already assign actual_type to new->type above. I think the dprintk
> needs actual_type and not what new->type has been changed to as that is
> in new_type.
>
Actually I have same questions. I find these output logs are added in commit:
6997ab4982a29925e79f72c3a59823cf944c3529(x86: add PAT related debug prints)
In the past, *new_type == actual_type == new->type on success. codes are below.
author use actual_type there.
376 if (ret_type) {
377 printk(
378 "reserve_memtype added 0x%Lx-0x%Lx, track %s, req %s, ret %s\n",
379 start, end, cattr_name(actual_type),
380 cattr_name(req_type), cattr_name(*ret_type));
381 } else {
382 printk(
383 "reserve_memtype added 0x%Lx-0x%Lx, track %s, req %s\n",
384 start, end, cattr_name(actual_type),
385 cattr_name(req_type));
386 }
But after reserve_memtype reworked, only new->type == *new_type on success.
actual_type is not synced with the them. So someone use new->type instead of
actual_type in dprintk.
I am not very clear why author need these debug information. So to avoid any
misunderstanding, I keep the same behavior of this dprintk. Keep what the
dpinrk does in the past.
If someone really think this debug information need change, maybe it's better
to send a new patch to fix it.
because *new_type is equal to new->type or new->type just did not change when
new_type is NULL. perhaps we can assign actual_type in such way below.
+ actual_type = new_type ? *new_type : actual_type;
thanks
xinxhui
>> + spin_unlock(&memtype_lock);
>> +
>> if (err) {
>> pr_info("x86/PAT: reserve_memtype failed [mem %#010Lx-%#010Lx],
>> track %s, req %s\n",
>> start, end - 1,
>> cattr_name(new->type), cattr_name(req_type));
>> kfree(new);
>> - spin_unlock(&memtype_lock);
>> -
>> return err;
>> }
>>
>> - spin_unlock(&memtype_lock);
>> -
>> dprintk("reserve_memtype added [mem %#010Lx-%#010Lx], track %s, req %s,
>> ret %s\n",
>> - start, end - 1, cattr_name(new->type), cattr_name(req_type),
>> + start, end - 1, cattr_name(actual_type), cattr_name(req_type),
>> new_type ? cattr_name(*new_type) : "-");
>>
>> return err;
>> --
>> 1.9.1
>
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