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    SubjectRe: [BUG] Lockless patches cause hardlock under heavy IO
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    On Sun, 2008-06-22 at 10:37 -0400, Ryan Hope wrote:
    > Well I couldn't stop playing with this... I am pretty sure the cause
    > of the hardlocks is in the second half of the patches (the speculative
    > page ref patches). I reversed all of those patches so that just the
    > GUP patchs were included and no more hardlocks... then I applied the
    > concurrent page cache patches from the -rt branch include 1 OLD
    > speculative page ref patch and this caused hardlocks for peopel again.
    > However enabling heap randomization fixed the hardlocks for one of the
    > users and the disabling swap fixed the issue of the other user. I hope
    > this helps.

    What are people doing to make it hang?

    > On Thu, Jun 19, 2008 at 4:19 AM, Nick Piggin <nickpiggin@yahoo.com.au> wrote:
    > > On Thursday 19 June 2008 18:12, Peter Zijlstra wrote:
    > >> On Wed, 2008-06-18 at 17:15 -0400, Ryan Hope wrote:
    > >> > I applied the following patches from 2.6-26-rc5-mm3 to 2.6.26-rc6 and
    > >> > they caused a hardlock under heavy IO:
    > >>
    > >> What kind of machine, how much memory, how many spindles, what
    > >> filesystem and what is heavy load?
    > >>
    > >> Furthermore, try the NMI watchdog with serial/net-console to capture its
    > >> output.
    > >
    > >
    > > Good suggestions. A trace would be really helpful.
    > >
    > > As Arjan suggested, debug options especially CONFIG_DEBUG_VM would be
    > > a good idea to turn on if you haven't already.
    > >
    > > BTW. what was the reason for applying those patches? Did you hit the
    > > problem with -mm also, and hope to narrow it down?
    > >
    > >
    > >> > x86-implement-pte_special.patch
    > >> > mm-introduce-get_user_pages_fast.patch
    > >> > mm-introduce-get_user_pages_fast-fix.patch
    > >> > mm-introduce-get_user_pages_fast-checkpatch-fixes.patch
    > >> > x86-lockless-get_user_pages_fast.patch
    > >> > x86-lockless-get_user_pages_fast-checkpatch-fixes.patch
    > >> > x86-lockless-get_user_pages_fast-fix.patch
    > >> > x86-lockless-get_user_pages_fast-fix-2.patch
    > >> > x86-lockless-get_user_pages_fast-fix-2-fix-fix.patch
    > >> > x86-lockless-get_user_pages_fast-fix-warning.patch
    > >> > dio-use-get_user_pages_fast.patch
    > >> > splice-use-get_user_pages_fast.patch
    > >> > x86-support-1gb-hugepages-with-get_user_pages_lockless.patch
    > >> > #
    > >> > mm-readahead-scan-lockless.patch
    > >> > radix-tree-add-gang_lookup_slot-gang_lookup_slot_tag.patch
    > >> > #mm-speculative-page-references.patch: clameter saw bustage
    > >> > mm-speculative-page-references.patch
    > >> > mm-speculative-page-references-fix.patch
    > >> > mm-speculative-page-references-fix-fix.patch
    > >> > mm-speculative-page-references-hugh-fix3.patch
    > >> > mm-lockless-pagecache.patch
    > >> > mm-spinlock-tree_lock.patch
    > >> > powerpc-implement-pte_special.patch
    > >> >
    > >> > I am on an x86_64. I dont know what other info you need...
    > >
    > > Can you isolate it to one of the two groups of patches? I suspect it
    > > might be the latter so you might try that first -- this version of
    > > speculative page references is very nice in theory but it is a little
    > > more complex to implement the slowpaths so it could be an error there.
    > >



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