Re: Bounce buffer deadlock

[Alan Cox]

> Has anyone else seen a hang like this:
> 
>   bdflush()
>     flush_dirty_buffers()
>       ll_rw_block()
> 	submit_bh(buffer X)
> 	  generic_make_request()
> 	    __make_request()
> 	        create_bounce()
> 		  alloc_bounce_page()
> 		    alloc_page()
> 		      try_to_free_pages()
> 			do_try_to_free_pages()
> 			  page_launder()
> 			    try_to_free_buffers( , 2)  -- i.e. wait for buffers
> 			      sync_page_buffers()
> 				__wait_on_buffer(buffer X)

Whoops. We actually carefully set PF_MEMALLOC to avoid deadlocks here but if
the buffer is laundered.... ummm

Looks like page_launder needs to be more careful

> I hit this in 2.4.6-pre6, and I don't see anything in the ac series to protect
> against it.

Not this one no

Alan