Messages in this thread | | | Date | Wed, 06 Nov 2002 18:51:07 -0800 | From | Andrew Morton <> | Subject | Re: PageLRU BUG() when preemption is turned on (2.4 kernel) |
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Jun Sun wrote: > > I am chasing a nasty bug that shows up in 2.4 kernel when preemption > is turned on. I would appreciate any help. Please cc your reply > to me email account. > > I caught the BUG() live with kgdb (on a MIPS board). See the backtrace > attached at the end. > > In a nutshell, access_process_vm() calls put_page(), which > calls __free_pages(), where it finds page->count is 0 but does not > like the fact that page->flags still has LRU bit set. >
That's a bug in older 2.4 kernels. You'll need to use a more recent kernel, or change that put_page() to be a page_cache_release(), or forward-port this chunk:
/* * Yes, think what happens when other parts of the kernel take * a reference to a page in order to pin it for io. -ben */ if (PageLRU(page)) { if (unlikely(in_interrupt())) BUG(); lru_cache_del(page); }
to your __free_pages_ok().
The problem is that `put_page()' doesn't know how to deal with the final release of a page which is on the LRU. Someone else released their reference, leaving access_process_vm() unexpectedly holding the last reference to the page. But it does put_page(), which then says "why didn't you remove this page from the LRU? BUG." - 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/
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