On Wed, 24 Oct 2007 16:39:57 -0400 Doug Reiland wrote:
> I have seen some hangs in 2.6-x86_64 in flush_kernel_map(). The tests
> cause alot of ioremap/iounmap to occur concurrently across many
> processor threads.
>
> Looking at the hung processor hangs, they are looping in
> flush_kernel_map() and the list they get from the smp_call_function()
> appears to be corrupt. In fact, I see deferred_pages as an entry and
> that isn't supposed to happen.
>
> I am questioning the locking in global_flush_tlb() listed below. The
> down_read/up_read protection doesn't seen safe. If several threads are
> rushing thru here, deferred_pages could be getting changed as they
> look at it. I don't think there any protection when
> list_replace_init() calls INIT_LIST_HEAD().
>
> I changed the down_read()/up_read() around list_replace_init() to
> down_write()/up_write() and my test runs fine.
>
>
> void global_flush_tlb(void)
> {
> struct page *pg, *next;
> struct list_head l;
>
> down_read(&init_mm.mmap_sem); // XXX should be down_write()???
> list_replace_init(&deferred_pages, &l);
> up_read(&init_mm.mmap_sem); // XXX should be up_write()????
> flush_map(&l);
>
> list_for_each_entry_safe(pg, next, &l, lru) {
> ClearPagePrivate(pg);
> __free_page(pg);
> }
> }
Seems to be already fixed in current git tree.
---
~Randy
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