On Thu, Feb 08, 2018 at 02:58:40PM +0800, Jason Wang wrote:
>
>
> On 2018年02月08日 12:45, Michael S. Tsirkin wrote:
> > On Thu, Feb 08, 2018 at 11:59:24AM +0800, Jason Wang wrote:
> > > This patch switch to use kvmalloc_array() for using a vmalloc()
> > > fallback to help in case kmalloc() fails.
> > >
> > > Reported-by: syzbot+e4d4f9ddd42955397...@syzkaller.appspotmail.com
> > > Fixes: 2e0ab8ca83c12 ("ptr_ring: array based FIFO for pointers")
> > I guess the actual patch is the one that switches tun to ptr_ring.
>
> I think not, since the issue was large allocation.
>
> >
> > In fact, I think the actual bugfix is patch 2/2. This specific one
> > just makes kmalloc less likely to fail but that's
> > not what syzbot reported.
>
> Agree.
>
> >
> > Then I would add this patch on top to make kmalloc less likely to fail.
>
> Ok.
>
> > > Signed-off-by: Jason Wang <jasow...@redhat.com>
> >
> >
> > > ---
> > > include/linux/ptr_ring.h | 10 +++++-----
> > > 1 file changed, 5 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> > > index 1883d61..2af71a7 100644
> > > --- a/include/linux/ptr_ring.h
> > > +++ b/include/linux/ptr_ring.h
> > > @@ -466,7 +466,7 @@ static inline int ptr_ring_consume_batched_bh(struct
> > > ptr_ring *r,
> > > static inline void **__ptr_ring_init_queue_alloc(unsigned int size,
> > > gfp_t gfp)
> > > {
> > > - return kcalloc(size, sizeof(void *), gfp);
> > > + return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO);
> > > }
> > > static inline void __ptr_ring_set_size(struct ptr_ring *r, int size)
> > This implies a bunch of limitations on the flags. From kvmalloc_node
> > docs:
> >
> > * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported.
> > * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc
> > is
> > * preferable to the vmalloc fallback, due to visible performance
> > drawbacks.
> >
> > Fine with all the current users, but if we go this way, please add
> > documentation so future users don't misuse this API.
>
> I suspect this is somehow a overkill since this means we need sync with
> mm/vmalloc changes in the future to keep it synced.
>
> > Alternatively, test flags and call kvmalloc or kcalloc?
>
> Similar to the above issue, I would rather leave it as is.
>
> Thanks
How do we prevent someone from inevitably trying to use this with
GFP_ATOMIC?
> >
> >
> > > @@ -601,7 +601,7 @@ static inline int ptr_ring_resize(struct ptr_ring *r,
> > > int size, gfp_t gfp,
> > > spin_unlock(&(r)->producer_lock);
> > > spin_unlock_irqrestore(&(r)->consumer_lock, flags);
> > > - kfree(old);
> > > + kvfree(old);
> > > return 0;
> > > }
> > > @@ -641,7 +641,7 @@ static inline int ptr_ring_resize_multiple(struct
> > > ptr_ring **rings,
> > > }
> > > for (i = 0; i < nrings; ++i)
> > > - kfree(queues[i]);
> > > + kvfree(queues[i]);
> > > kfree(queues);
> > > @@ -649,7 +649,7 @@ static inline int ptr_ring_resize_multiple(struct
> > > ptr_ring **rings,
> > > nomem:
> > > while (--i >= 0)
> > > - kfree(queues[i]);
> > > + kvfree(queues[i]);
> > > kfree(queues);
> > > @@ -664,7 +664,7 @@ static inline void ptr_ring_cleanup(struct ptr_ring
> > > *r, void (*destroy)(void *))
> > > if (destroy)
> > > while ((ptr = ptr_ring_consume(r)))
> > > destroy(ptr);
> > > - kfree(r->queue);
> > > + kvfree(r->queue);
> > > }
> > > #endif /* _LINUX_PTR_RING_H */
> > > --
> > > 2.7.4
