Re: [Bug 192571] zswap + zram enabled BUG

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

On (01/18/17 20:36), Dan Streetman wrote:
> On Wed, Jan 18, 2017 at 8:17 AM, Michal Hocko <mhocko@kernel.org> wrote:
> > On Wed 18-01-17 10:39:48, Sergey Senozhatsky wrote:
> >> Cc Dan
> >>
> >> On (01/17/17 12:22), Andrew Morton wrote:
> >> > > https://bugzilla.kernel.org/show_bug.cgi?id=192571
> >> > >
> >> > > --- Comment #1 from Gluzskiy Alexandr <sss123next@list.ru> ---
> >> > > [199961.576604] ------------[ cut here ]------------
> >> > > [199961.577830] kernel BUG at mm/zswap.c:1108!
> >>
> >> zswap didn't manage to decompress the page:
> >>
> >> static int zswap_frontswap_load(unsigned type, pgoff_t offset,
> >>                               struct page *page)
> >> {
> >> ...
> >>       dst = kmap_atomic(page);
> >>       tfm = *get_cpu_ptr(entry->pool->tfm);
> >>       ret = crypto_comp_decompress(tfm, src, entry->length, dst, &dlen);
> >>       put_cpu_ptr(entry->pool->tfm);
> >>       kunmap_atomic(dst);
> >>       zpool_unmap_handle(entry->pool->zpool, entry->handle);
> >>       BUG_ON(ret);
> >>       ^^^^^^^^^^^
> >
> > Ugh, why do we even do that? This is not the way how to handle error
> > situations. AFAIU propagating the error out wouldn't be a big deal
> > because we would just fallback to regular swap, right?
> 
> yeah this function definitely should never bug; it's just a callback
> from the zpool to try to write a page back to the swapcache so the
> zpool can free a page.  It's definitely ok for it to return an error.
> 

good. Dan, Seth, care to send the patch?
and one more thing... can you take a look at [1]?

[1] https://marc.info/?l=linux-mm&m=147031191906154&w=4

	-ss

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