Re: [bug report] RDMA: Convert put_page() to put_user_page*()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Feb 24, 2022 at 12:37:58PM +0300, Dan Carpenter wrote:
> Hi John,
> 
> I'm not really sure who to send this bug report to so you got picked
> a bit at random...
> 
> The patch ea996974589e: "RDMA: Convert put_page() to
> put_user_page*()" from May 24, 2019, leads to the following Smatch
> static checker warning:
> 
> 	./include/linux/pagemap.h:897 folio_lock()
> 	warn: sleeping in atomic context
> 
> ./include/linux/pagemap.h
>     895 static inline void folio_lock(struct folio *folio)
>     896 {
>     898         if (!folio_trylock(folio))
>     899                 __folio_lock(folio);
>     900 }
> 
> The problem is that unpin_user_pages_dirty_lock() calls folio_lock()
> which can sleep.
> 
> Here is the raw Smatch preempt output.  As you can see there are
> several places which seem to call unpin_user_pages_dirty_lock() with
> preempt disabled.
> 
> __usnic_uiom_reg_release() <- disables preempt
> usnic_uiom_reg_get() <- disables preempt
> -> usnic_uiom_put_pages()
> rds_tcp_write_space() <- disables preempt
> -> rds_send_path_drop_acked()
>    -> rds_send_remove_from_sock()
>       -> rds_message_put()
>          -> rds_message_purge()
>             -> rds_rdma_free_op()
> rds_message_purge() <duplicate>
> -> rds_atomic_free_op()
>                -> unpin_user_pages_dirty_lock()
>                   -> folio_lock()
> 
> Let's pull out the first example:
> 
> drivers/infiniband/hw/usnic/usnic_uiom.c
>    228                spin_lock(&pd->lock);
>    229                usnic_uiom_remove_interval(&pd->root, vpn_start,
>    230                                                vpn_last, &rm_intervals);
>    231                usnic_uiom_unmap_sorted_intervals(&rm_intervals, pd);
>    232
>    233                list_for_each_entry_safe(interval, tmp, &rm_intervals, link) {
>    234                        if (interval->flags & IOMMU_WRITE)
>    235                                writable = 1;
>    236                        list_del(&interval->link);
>    237                        kfree(interval);
>    238                }
>    239
>    240                usnic_uiom_put_pages(&uiomr->chunk_list, dirty & writable);
>                       ^^^^^^^^^^^^^^^^^^^^
> We're holding a spin lock, but _put_pages() calls unpin_user_pages_dirty_lock().
> 
>    241                spin_unlock(&pd->lock);
>    242        }


Huh. So yes, these drivers are broken and always have been. They will
crash if userspace feeds them file backed memory or something.

Probably best to send this report to each of the top level driver
maintainers

Jason