The patch titled lockdep: annotate epoll has been added to the -mm tree. Its filename is lockdep-annotate-epoll.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: lockdep: annotate epoll From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> On Sat, 2008-01-05 at 13:35 -0800, Davide Libenzi wrote: > I remember I talked with Arjan about this time ago. Basically, since 1) > you can drop an epoll fd inside another epoll fd 2) callback-based wakeups > are used, you can see a wake_up() from inside another wake_up(), but they > will never refer to the same lock instance. > Think about: > > dfd = socket(...); > efd1 = epoll_create(); > efd2 = epoll_create(); > epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); > epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); > > When a packet arrives to the device underneath "dfd", the net code will > issue a wake_up() on its poll wake list. Epoll (efd1) has installed a > callback wakeup entry on that queue, and the wake_up() performed by the > "dfd" net code will end up in ep_poll_callback(). At this point epoll > (efd1) notices that it may have some event ready, so it needs to wake up > the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() > that ends up in another wake_up(), after having checked about the > recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to > avoid stack blasting. Never hit the same queue, to avoid loops like: > > epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); > epoll_ctl(efd3, EPOLL_CTL_ADD, efd2, ...); > epoll_ctl(efd4, EPOLL_CTL_ADD, efd3, ...); > epoll_ctl(efd1, EPOLL_CTL_ADD, efd4, ...); > > The code "if (tncur->wq == wq || ..." prevents re-entering the same > queue/lock. Since the epoll code is very careful to not nest same instance locks allow the recursion. Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Tested-by: Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx> Acked-by: Davide Libenzi <davidel@xxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/eventpoll.c | 2 +- include/linux/wait.h | 16 ++++++++++++++++ 2 files changed, 17 insertions(+), 1 deletion(-) diff -puN fs/eventpoll.c~lockdep-annotate-epoll fs/eventpoll.c --- a/fs/eventpoll.c~lockdep-annotate-epoll +++ a/fs/eventpoll.c @@ -353,7 +353,7 @@ static void ep_poll_safewake(struct poll spin_unlock_irqrestore(&psw->lock, flags); /* Do really wake up now */ - wake_up(wq); + wake_up_nested(wq, 1 + wake_nests); /* Remove the current task from the list */ spin_lock_irqsave(&psw->lock, flags); diff -puN include/linux/wait.h~lockdep-annotate-epoll include/linux/wait.h --- a/include/linux/wait.h~lockdep-annotate-epoll +++ a/include/linux/wait.h @@ -161,6 +161,22 @@ wait_queue_head_t *FASTCALL(bit_waitqueu #define wake_up_locked(x) __wake_up_locked((x), TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE) #define wake_up_interruptible_sync(x) __wake_up_sync((x),TASK_INTERRUPTIBLE, 1) +#ifdef CONFIG_DEBUG_LOCK_ALLOC +/* + * macro to avoid include hell + */ +#define wake_up_nested(x, s) \ +do { \ + unsigned long flags; \ + \ + spin_lock_irqsave_nested(&(x)->lock, flags, (s)); \ + wake_up_locked(x); \ + spin_unlock_irqrestore(&(x)->lock, flags); \ +} while (0) +#else +#define wake_up_nested(x, s) wake_up(x) +#endif + #define __wait_event(wq, condition) \ do { \ DEFINE_WAIT(__wait); \ _ Patches currently in -mm which might be from a.p.zijlstra@xxxxxxxxx are origin.patch lockdep-annotate-epoll.patch git-sched.patch slub-move-kmem_cache_node-determination-into-add_full-and-add_partial-slub-workaround-for-lockdep-confusion.patch swapin-needs-gfp_mask-for-loop-on-tmpfs.patch mm-page-writeback-highmem_is_dirtyable-option.patch mm-page-writeback-highmem_is_dirtyable-option-fix.patch skip-writing-data-pages-when-inode-is-under-i_sync.patch fix-dirty-page-accounting-leak-with-ext3-data=journal.patch kernel-add-mutex_lock_killable.patch vfs-use-mutex_lock_killable-in-vfs_readdir.patch memory-controller-add-documentation.patch memory-controller-resource-counters-v7.patch memory-controller-containers-setup-v7.patch memory-controller-accounting-setup-v7.patch memory-controller-memory-accounting-v7.patch memory-controller-task-migration-v7.patch memory-controller-add-per-container-lru-and-reclaim-v7.patch memory-controller-improve-user-interface.patch memory-controller-oom-handling-v7.patch memory-controller-add-switch-to-control-what-type-of-pages-to-limit-v7.patch memory-controller-make-page_referenced-container-aware-v7.patch memory-controller-make-charging-gfp-mask-aware.patch memcgroup-reinstate-swapoff-mod.patch bugfix-for-memory-cgroup-controller-charge-refcnt-race-fix.patch bugfix-for-memory-cgroup-controller-fix-error-handling-path-in-mem_charge_cgroup.patch bugfix-for-memory-controller-add-helper-function-for-assigning-cgroup-to-page.patch bugfix-for-memory-cgroup-controller-migration-under-memory-controller-fix.patch bugfix-for-memory-cgroup-controller-avoid-pagelru-page-in-mem_cgroup_isolate_pages.patch bugfix-for-memory-cgroup-controller-avoid-pagelru-page-in-mem_cgroup_isolate_pages-fix.patch memcgroup-fix-zone-isolation-oom.patch memcgroup-revert-swap_state-mods.patch memory-cgroup-enhancements-fix-zone-handling-in-try_to_free_mem_cgroup_page.patch memory-cgroup-enhancements-force_empty-interface-for-dropping-all-account-in-empty-cgroup.patch memory-cgroup-enhancements-remember-a-page-is-charged-as-page-cache.patch memory-cgroup-enhancements-remember-a-page-is-on-active-list-of-cgroup-or-not.patch memory-cgroup-enhancements-add-status-accounting-function-for-memory-cgroup.patch memory-cgroup-enhancements-add-memorystat-file.patch memory-cgroup-enhancements-add-pre_destroy-handler.patch memory-cgroup-enhancements-implicit-force_empty-at-rmdir.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-add-scan_global_lru-macro.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-nid-zid-helper-function-for-cgroup.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-per-zone-active-inactive-counter.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-calculate-mapper_ratio-per-cgroup.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-calculate-active-inactive-imbalance-per-cgroup.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-remember-reclaim-priority-in-memory-cgroup.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-calculate-the-number-of-pages-to-be-scanned-per-cgroup.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-modifies-vmscanc-for-isolate-globa-cgroup-lru-activity.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-per-zone-lru-for-cgroup.patch per-zone-and-reclaim-enhancements-for-memory-controller-take-3-per-zone-lock-for-cgroup.patch - To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html