On Thu, 31 Jan 2008, Andrea Arcangeli wrote: > > Hmmmm.. exit_mmap is only called when the last reference is removed > > against the mm right? So no tasks are running anymore. No pages are left. > > Do we need to serialize at all for mmu_notifier_release? > > KVM sure doesn't need any locking there. I thought somebody had to > possibly take a pin on the "mm_count" and pretend to call > mmu_notifier_register at will until mmdrop was finally called, in a > out of order fashion given mmu_notifier_release was implemented like > if the list could change from under it. Note mmdrop != mmput. mmput > and in turn mm_users is the serialization point if you prefer to drop > all locking from _release. Nobody must ever attempt a mmu_notifier_* > after calling mmput for that mm. That should be enough to be > safe. I'm fine either ways...
exit_mmap (where we call invalidate_all() and release()) is called when mm_users == 0: void mmput(struct mm_struct *mm) { might_sleep(); if (atomic_dec_and_test(&mm->mm_users)) { exit_aio(mm); exit_mmap(mm); if (!list_empty(&mm->mmlist)) { spin_lock(&mmlist_lock); list_del(&mm->mmlist); spin_unlock(&mmlist_lock); } put_swap_token(mm); mmdrop(mm); } } EXPORT_SYMBOL_GPL(mmput); So there is only a single thread executing at the time when invalidate_all() is called from exit_mmap(). Then we drop the pages, and the page tables. After the page tables we call the ->release method and then remove the vmas. So even dropping off the mmu_notifier chain in invalidate_all() could be done without an issue and without locking. Trouble is if other callbacks attempt the same. Do we need to support the removal from the mmu_notifier list in invalidate_range()? ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel