Messages in this thread | | | Date | Mon, 18 Dec 2006 20:42:04 +1100 | From | Nick Piggin <> | Subject | Re: 2.6.19 file content corruption on ext3 |
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Andrew Morton wrote: > On Mon, 18 Dec 2006 18:22:42 +1100 > Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>>Yes I could believe it the corruption is caused by something else >>completely. > > > Think so. We do have a problem here, but only on threaded apps, I believe. > rtorrent doesn't appear to be threaded, and the bug is hit on non-preempt > UP.
I think (see below) that it does not apply only to threaded apps. But it would need one of SMP or PREEMPT to trigger.
>>After try_to_free_buffers detaches the buffers from the page, a >>pagefault can come in, and mark the pte writeable, then set_page_dirty >>(which finds no buffers, so only sets PG_dirty). >> >>The page can now get dirtied through this mapping. >> >>try_to_free_buffers then goes on to clean the page and ptes. > > > try_to_free_buffers() isn't called against a page which doesn't have > buffers. It'll oops.
Sure. But I think the race exists... I'll try spelling it out in the conventional way:
try_to_free_buffers() drop_buffers() (succeeds)
** preempt here or run right-hand thread on 2nd CPU in SMP **
do_no_page() set_page_dirty()
[now modify the page via this mapping (from this process or a concurrent thread)]
clear_page_dirty() (clears PG_dirty + pte dirty, oops)
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