Messages in this thread | | | Date | Wed, 3 Jan 2007 21:41:21 -0800 | From | Andrew Morton <> | Subject | Re: VM: Fix nasty and subtle race in shared mmap'ed page writeback |
| |
On Wed, 3 Jan 2007 20:44:36 -0800 (PST) Linus Torvalds <torvalds@osdl.org> wrote:
> Actually, I think 2.6.18 may have a subtle variation on it. > > In particular, I look back at the try_to_free_buffers() thing that I hated > so much, and it makes me wonder.. It used to do: > > spin_lock(&mapping->private_lock); > ret = drop_buffers(page, &buffers_to_free); > spin_unlock(&mapping->private_lock); > if (ret) { > .. crappy comment .. > if (test_clear_page_dirty(page)) > task_io_account_cancelled_write(PAGE_CACHE_SIZE); > } > > and I think that at least on SMP, we had a race with another CPU doing the > "mark page dirty if it was dirty in the PTE" at the same time. Because the > marking dirty would come in, find no buffers (they just got dropped), and > then mark the page dirty (ignoring the lack of any buffers), but then the > above would do the "test_clear_page_dirty()" thing on it. >
That bug was introduced in 2.6.19, with the dirty page tracking patches.
2.6.18 and earlier used ->private_lock coverage in try_to_free_buffers() to prevent it.
> Ie the race, I think, existed where that crappy comment was.
The comment was complete, accurate and needed. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |