Messages in this thread | | | Date | Wed, 31 May 2006 10:21:55 +1000 | From | Nick Piggin <> | Subject | Re: [rfc][patch] remove racy sync_page? |
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Hugh Dickins wrote: > On Tue, 30 May 2006, Nick Piggin wrote: > >>But for 2.6.17, how's this? > > > It was a great emperor's-clothes-like discovery. But we've survived > for so many years without noticing, does it have to be fixed right > now for 2.6.17? (I bet I'd be insisting yes if I'd found it.)
It's up to Linus and Andrew I guess. I don't see why not, but I don't much care one way or the other. But thanks having a quick look at it, we may want it for the Suse kernel.
> > The thing I don't like about your lock_page_nosync (reasonable as > it is) is that the one case you're using it, set_page_dirty_nolock, > would be so much happier not to have to lock the page in the first > place - it's only doing _that_ to stabilize page->mapping, and the > lock_page forbids it from being called from anywhere that can't > sleep, which is often just where we want to call it from. Neil's > suggestion, using a spin_lock against the mapping changing, would > help there; but seems like more work than I'd want to get into.
But making PG_lock a spinning lock is completely unrelated to the bug at hand.
> > So, although I think lock_page_nosync fixes the bug (at least in > that one place we've identified there's likely to be such a bug), > it seems to be aiming at the wrong target. I'm pacing and thinking, > doubt I'll come up with anything better, please don't hold breath.
It is the correct target. I know all about your set_page_dirty_lock problems, but they aren't what I'm trying to fix.
AFAIKS, you could also make set_page_dirty_lock non sleeping quite easily by making inode slabs RCU freed.
What places want to use set_page_dirty_lock without sleeping? The only place in drivers/ apart from sg/st that SetPageDirty are rd.c and via_dmablit.c, both of which look OK, if a bit crufty.
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