Re: [PATCH 1/1] ipc/shm: fix the historical/wrong mm->start_stack check

[Cyrill Gorcunov]

On Sat, Aug 23, 2014 at 04:43:27PM +0200, Oleg Nesterov wrote:
> The ->start_stack check in do_shmat() looks ugly and simply wrong.
> 
> 1. ->start_stack is only valid right after exec(), the application
>    can switch to another stack and even unmap this area.
> 
> 2. The reason for this check is not clear at all. The application
>    should know what it does. And why 4 pages? And why in fact it
>    requires 5 pages?
> 
> 3. This wrongly assumes that the stack can only grown down.
> 
> Personally I think we should simply kill this check, but I did not
> dare to do this. So the patch only fixes the 1st problem (mostly to
> avoid the usage of mm->start_stack) and ignores VM_GROWSUP.
> 
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx>

I don't understand this check either, the comment above it says nothing
but only commits what code is doing not explaining why.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/