Messages in this thread |  | | Date | Sun, 18 Nov 2001 07:37:30 +0100 | From | Andrea Arcangeli <> | Subject | Re: VM-related Oops: 2.4.15pre1 |
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On Sat, Nov 17, 2001 at 10:24:44PM -0800, Linus Torvalds wrote: > > On Sun, 18 Nov 2001, Andrea Arcangeli wrote: > > > > I also agree the patch shouldn't matter, but one suspect thing is the > > fact add_to_swap_cache goes to clobber in a non atomic manner the page > > lock. > > .. you mean __add_to_page_cache(), not add_to_swap_cache(). > > And nope, not really. It does use plain stores to page->flags, and I agree > that it is ugly, but if the page was locked before calling it, all the > stores will be with the PG_lock bit set - and even plain stores _are_ > documented to be atomic on x86 (and on all other reasonable architectures > too).
I know all is right if GCC just overwrites the page->flags with data that keeps PG_locked set. But GCC doesn't guarantee that. GCC can as well do:
flags = page->flags; page->flags = 0;
change flags here
page->flags = flags
probably gcc doesn't, but that's still a kernel bug.
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