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    SubjectRe: [PATCH v5 00/13] lockdep: Implement crossrelease feature
    On Wed, Jan 18, 2017 at 10:17:26PM +0900, Byungchul Park wrote:
    > I checked if crossrelease feature works well on my qemu-i386 machine.
    > There's no problem at all to work on mine. But I wonder if it's also
    > true even on other machines. Especially, on large system. Could you
    > let me know if it doesn't work on yours? Or Could you let me know if
    > crossrelease feature is useful? Please let me know if you need to
    > backport it to another version but it's not easy. Then I can provide
    > the backported version after working it.

    Hello peterz,

    I don't want to rush you, but I think enough time has passed. Could you
    check this? I tried to apply what you recommanded at the previous spin
    as much as possible. Could you?

    Thanks,
    Byungchul

    >
    > -----8<-----
    >
    > Change from v4
    > - rebase on vanilla v4.9 tag
    > - re-name pend_lock(plock) to hist_lock(xhlock)
    > - allow overwriting ring buffer for hist_lock
    > - unwind ring buffer instead of tagging id for each irq
    > - introduce lockdep_map_cross embedding cross_lock
    > - make each work of workqueue distinguishable
    > - enhance comments
    > (I will update the document at the next spin.)
    >
    > Change from v3
    > - reviced document
    >
    > Change from v2
    > - rebase on vanilla v4.7 tag
    > - move lockdep data for page lock from struct page to page_ext
    > - allocate plocks buffer via vmalloc instead of in struct task
    > - enhanced comments and document
    > - optimize performance
    > - make reporting function crossrelease-aware
    >
    > Change from v1
    > - enhanced the document
    > - removed save_stack_trace() optimizing patch
    > - made this based on the seperated save_stack_trace patchset
    > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1182242.html
    >
    > Can we detect deadlocks below with original lockdep?
    >
    > Example 1)
    >
    > PROCESS X PROCESS Y
    > -------------- --------------
    > mutext_lock A
    > lock_page B
    > lock_page B
    > mutext_lock A // DEADLOCK
    > unlock_page B
    > mutext_unlock A
    > mutex_unlock A
    > unlock_page B
    >
    > where A and B are different lock classes.
    >
    > No, we cannot.
    >
    > Example 2)
    >
    > PROCESS X PROCESS Y PROCESS Z
    > -------------- -------------- --------------
    > mutex_lock A
    > lock_page B
    > lock_page B
    > mutext_lock A // DEADLOCK
    > mutext_unlock A
    > unlock_page B
    > (B was held by PROCESS X)
    > unlock_page B
    > mutex_unlock A
    >
    > where A and B are different lock classes.
    >
    > No, we cannot.
    >
    > Example 3)
    >
    > PROCESS X PROCESS Y
    > -------------- --------------
    > mutex_lock A
    > mutex_lock A
    > wait_for_complete B // DEADLOCK
    > mutex_unlock A
    > complete B
    > mutex_unlock A
    >
    > where A is a lock class and B is a completion variable.
    >
    > No, we cannot.
    >
    > Not only lock operations, but also any operations causing to wait or
    > spin for something can cause deadlock unless it's eventually *released*
    > by someone. The important point here is that the waiting or spinning
    > must be *released* by someone.
    >
    > Using crossrelease feature, we can check dependency and detect deadlock
    > possibility not only for typical lock, but also for lock_page(),
    > wait_for_xxx() and so on, which might be released in any context.
    >
    > See the last patch including the document for more information.
    >
    > Byungchul Park (13):
    > lockdep: Refactor lookup_chain_cache()
    > lockdep: Fix wrong condition to print bug msgs for
    > MAX_LOCKDEP_CHAIN_HLOCKS
    > lockdep: Add a function building a chain between two classes
    > lockdep: Refactor save_trace()
    > lockdep: Pass a callback arg to check_prev_add() to handle stack_trace
    > lockdep: Implement crossrelease feature
    > lockdep: Make print_circular_bug() aware of crossrelease
    > lockdep: Apply crossrelease to completions
    > pagemap.h: Remove trailing white space
    > lockdep: Apply crossrelease to PG_locked locks
    > lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked
    > lockdep: Move data of CONFIG_LOCKDEP_PAGELOCK from page to page_ext
    > lockdep: Crossrelease feature documentation
    >
    > Documentation/locking/crossrelease.txt | 1053 ++++++++++++++++++++++++++++++++
    > include/linux/completion.h | 118 +++-
    > include/linux/irqflags.h | 24 +-
    > include/linux/lockdep.h | 129 ++++
    > include/linux/mm_types.h | 4 +
    > include/linux/page-flags.h | 43 +-
    > include/linux/page_ext.h | 4 +
    > include/linux/pagemap.h | 124 +++-
    > include/linux/sched.h | 9 +
    > kernel/exit.c | 9 +
    > kernel/fork.c | 23 +
    > kernel/locking/lockdep.c | 763 ++++++++++++++++++++---
    > kernel/sched/completion.c | 54 +-
    > kernel/workqueue.c | 1 +
    > lib/Kconfig.debug | 30 +
    > mm/filemap.c | 76 ++-
    > mm/page_ext.c | 4 +
    > 17 files changed, 2324 insertions(+), 144 deletions(-)
    > create mode 100644 Documentation/locking/crossrelease.txt
    >
    > --
    > 1.9.1

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