Re: [PATCH v4 1/3] mm/vmap: keep track of free blocks for vmap allocation

[Uladzislau Rezki]

+Tobin C. Harding <tobin@xxxxxxxxxx>

On Wed, May 15, 2019 at 5:24 PM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
>
> Hello, Andrew.
>
> > An earlier version of this patch was accused of crashing the kernel:
> >
> > https://lists.01.org/pipermail/lkp/2019-April/010004.html
> >
> > does the v4 series address this?
> I tried before to narrow down that crash but i did not succeed, so
> i have never seen that before on my test environment as well as
> during running lkp-tests including trinity test case:
>
> test-url: http://codemonkey.org.uk/projects/trinity/
>
> But after analysis of the Call-trace and slob_alloc():
>
> <snip>
> [    0.395722] Call Trace:
> [    0.395722]  slob_alloc+0x1c9/0x240
> [    0.395722]  kmem_cache_alloc+0x70/0x80
> [    0.395722]  acpi_ps_alloc_op+0xc0/0xca
> [    0.395722]  acpi_ps_get_next_arg+0x3fa/0x6ed
> <snip>
>
> <snip>
>     /* Attempt to alloc */
>     prev = sp->lru.prev;
>     b = slob_page_alloc(sp, size, align);
>     if (!b)
>         continue;
>
>     /* Improve fragment distribution and reduce our average
>      * search time by starting our next search here. (see
>      * Knuth vol 1, sec 2.5, pg 449) */
>     if (prev != slob_list->prev &&
>             slob_list->next != prev->next)
>         list_move_tail(slob_list, prev->next); <- Crash is here in __list_add_valid()
>     break;
> }
> <snip>
>
> i see that it tries to manipulate with "prev" node that may be removed
> from the list by slob_page_alloc() earlier if whole page is used. I think
> that crash has to be fixed by the below commit:
>
> https://www.spinics.net/lists/mm-commits/msg137923.html
>
> it was introduced into 5.1-rc3 kernel.
>
> Why ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
> was accused is probably because it uses "kmem cache allocations with struct alignment"
> instead of kmalloc()/kzalloc(). Maybe because of bigger size requests
> it became easier to trigger the BUG. But that is theory.
>
> --
> Vlad Rezki



-- 
Uladzislau Rezki