Messages in this thread Patch in this message | | | Date | Mon, 24 Feb 2003 21:45:43 -0800 | From | Andrew Morton <> | Subject | Re: [OOPS] 2.5.63 - NULL pointer dereference in loop device |
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Jonah Sherman <jsherman@stuy.edu> wrote: > > I have come across a bug in the loop driver.
So you have. See, the `dd' fills the machine up with dirty memory and the loop driver wants to take a copy of all that memory to write it out. It takes this copy inside page reclaim, where we are allowed to use *all* memory.
So obviously, as there is so much memory to be written, we just run out of the stuff.
The loop driver has a tendency to do this sort of thing. Whenever it does, we slap another bandaid on it.
diff -puN drivers/block/loop.c~loop-hack drivers/block/loop.c --- 25/drivers/block/loop.c~loop-hack 2003-02-24 21:21:11.000000000 -0800 +++ 25-akpm/drivers/block/loop.c 2003-02-24 21:45:13.000000000 -0800 @@ -447,7 +447,22 @@ static struct bio *loop_get_buffer(struc goto out_bh; } - bio = bio_copy(rbh, GFP_NOIO, rbh->bi_rw & WRITE); + /* + * When called on the page reclaim -> writepage path, this code can + * trivially consume all memory. So we drop PF_MEMALLOC to avoid + * stealing all the page reserves and throttle to the writeout rate. + * pdflush will have been woken by page reclaim. Let it do its work. + */ + do { + int flags = current->flags; + + current->flags &= ~PF_MEMALLOC; + bio = bio_copy(rbh, (GFP_ATOMIC & ~__GFP_HIGH) | __GFP_NOWARN, + rbh->bi_rw & WRITE); + current->flags = flags; + if (bio == NULL) + blk_congestion_wait(WRITE, HZ/10); + } while (bio == NULL); bio->bi_end_io = loop_end_io_transfer; bio->bi_private = rbh; _
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