On Thu, Jun 02, 2011 at 10:29:39AM -0700, Hugh Dickins wrote: > AndreaA, I didn't study the patch you posted half an hour ago, > since by that time I'd worked it out and was preparing patch below. > I think your patch would be for a different bug, hopefully one we > don't have, it looks more complicated than we should need for this. I didn't expect two different bugs leading to double free. If you've time please review my other patch too because mmput runs with no mmap_sem hold and I think the ksm scan code runs under the assumption that __ksm_exit is waiting in down_write() when ksm_mmlist_lock is released (before freeing the mm_slot), and that assumption is wrong. ksm_test_exit may very well be true despite __ksm_exit didn't run yet, and ksm scan will proceed freeing after changing the mm_slot and ksm_exit will be free to run and free again immediately after the ksm scan releases the ksm_mmlist_lock and before it clears the MMF_VM_MERGEABLE (because the mm_slot has been changed before releasing the ksm_mmlist_lock). The rmap_list being null will kind of hide it, the fact there's so little time between the unlock of the ksm_mmlist_lock and the clearing of MMF_VM_MERGEABLE (that will stop ksm_exit from calling __ksm_exit at all) will also hide it. At least in unmerge_and_remove_all_rmap_items remove_trailing_rmap_items will nuke the rmap_list just before this race runs so making it more likely possible. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>