Messages in this thread | | | Date | Sun, 25 Mar 2001 00:13:38 +0000 | From | "Stephen C. Tweedie" <> | Subject | Re: [PATCH] Fix races in 2.4.2-ac22 SysV shared memory |
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Hi,
On Fri, Mar 23, 2001 at 11:58:50AM -0800, Linus Torvalds wrote:
> Ehh.. Sleeping with the spin-lock held? Sounds like a truly bad idea.
Uggh --- the shmem code already does, see:
shmem_truncate->shmem_truncate_part->shmem_free_swp-> lookup_swap_cache->find_lock_page
It looks messy: lookup_swap_cache seems to be abusing the page lock gratuitously, but there are probably callers of it which rely on the assumption that it performs an implicit wait_on_page().
Rik, do you think it is really necessary to take the page lock and release it inside lookup_swap_cache? I may be overlooking something, but I can't see the benefit of it --- we can still race against page_launder, so the page may still get locked behind our backs after we get the reference from lookup_swap_cache (page_launder explicitly avoids taking the pagecache hash spinlock which might avoid this particular race).
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