diff options
| -rw-r--r-- | mm/mmu_notifier.c | 79 |
1 files changed, 39 insertions, 40 deletions
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index be04122fb27..6725ff18337 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -40,48 +40,44 @@ void __mmu_notifier_release(struct mm_struct *mm) int id; /* - * srcu_read_lock() here will block synchronize_srcu() in - * mmu_notifier_unregister() until all registered - * ->release() callouts this function makes have - * returned. + * SRCU here will block mmu_notifier_unregister until + * ->release returns. */ id = srcu_read_lock(&srcu); + hlist_for_each_entry_rcu(mn, &mm->mmu_notifier_mm->list, hlist) + /* + * If ->release runs before mmu_notifier_unregister it must be + * handled, as it's the only way for the driver to flush all + * existing sptes and stop the driver from establishing any more + * sptes before all the pages in the mm are freed. + */ + if (mn->ops->release) + mn->ops->release(mn, mm); + srcu_read_unlock(&srcu, id); + spin_lock(&mm->mmu_notifier_mm->lock); while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) { mn = hlist_entry(mm->mmu_notifier_mm->list.first, struct mmu_notifier, hlist); - /* - * Unlink. This will prevent mmu_notifier_unregister() - * from also making the ->release() callout. + * We arrived before mmu_notifier_unregister so + * mmu_notifier_unregister will do nothing other than to wait + * for ->release to finish and for mmu_notifier_unregister to + * return. */ hlist_del_init_rcu(&mn->hlist); - spin_unlock(&mm->mmu_notifier_mm->lock); - - /* - * Clear sptes. (see 'release' description in mmu_notifier.h) - */ - if (mn->ops->release) - mn->ops->release(mn, mm); - - spin_lock(&mm->mmu_notifier_mm->lock); } spin_unlock(&mm->mmu_notifier_mm->lock); /* - * All callouts to ->release() which we have done are complete. - * Allow synchronize_srcu() in mmu_notifier_unregister() to complete - */ - srcu_read_unlock(&srcu, id); - - /* - * mmu_notifier_unregister() may have unlinked a notifier and may - * still be calling out to it. Additionally, other notifiers - * may have been active via vmtruncate() et. al. Block here - * to ensure that all notifier callouts for this mm have been - * completed and the sptes are really cleaned up before returning - * to exit_mmap(). + * synchronize_srcu here prevents mmu_notifier_release from returning to + * exit_mmap (which would proceed with freeing all pages in the mm) + * until the ->release method returns, if it was invoked by + * mmu_notifier_unregister. + * + * The mmu_notifier_mm can't go away from under us because one mm_count + * is held by exit_mmap. */ synchronize_srcu(&srcu); } @@ -292,31 +288,34 @@ void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm) { BUG_ON(atomic_read(&mm->mm_count) <= 0); - spin_lock(&mm->mmu_notifier_mm->lock); if (!hlist_unhashed(&mn->hlist)) { + /* + * SRCU here will force exit_mmap to wait for ->release to + * finish before freeing the pages. + */ int id; + id = srcu_read_lock(&srcu); /* - * Ensure we synchronize up with __mmu_notifier_release(). + * exit_mmap will block in mmu_notifier_release to guarantee + * that ->release is called before freeing the pages. */ - id = srcu_read_lock(&srcu); - - hlist_del_rcu(&mn->hlist); - spin_unlock(&mm->mmu_notifier_mm->lock); - if (mn->ops->release) mn->ops->release(mn, mm); + srcu_read_unlock(&srcu, id); + spin_lock(&mm->mmu_notifier_mm->lock); /* - * Allow __mmu_notifier_release() to complete. + * Can not use list_del_rcu() since __mmu_notifier_release + * can delete it before we hold the lock. */ - srcu_read_unlock(&srcu, id); - } else + hlist_del_init_rcu(&mn->hlist); spin_unlock(&mm->mmu_notifier_mm->lock); + } /* - * Wait for any running method to finish, including ->release() if it - * was run by __mmu_notifier_release() instead of us. + * Wait for any running method to finish, of course including + * ->release if it was run by mmu_notifier_relase instead of us. */ synchronize_srcu(&srcu); |