On Thu, Mar 08, 2012 at 01:02:56PM -0800, Andrew Morton wrote: > > This fix the below lockdep warning > > OK, what's going on here. Deadlock in hugetlbfs mmap getting misreported. One last time: ->mmap_sem nests inside ->i_mutex. Both for regular files and for directories. Always had. For directories there's copy_to_user() from ->readdir() done under ->i_mutex. For regular files there's copy_from_user() from ->write(), usually done under ->i_mutex. On hugetlbfs there's copy_to_user() from ->read() done under ->i_mutex. It had not changed at all. Lockdep sees both call chains; the only question is which chain is seen first. And usually reading a directory happens earlier in the boot than writing into a file. That's all there is to it. Unfortunately, the fact that call chain being reported is obviously about directories leads to false hopes that deadlock doesn't exist - mmap() obviously can't happen to a directory inode, so people hope that it's a false positive. It isn't. Patch separating directory and non-directory ->i_mutex into different classes went in at some point, precisely due to those hopes. It had a braino that made it useless. Fix for that braino had been posted and sits my queue; I'll push it to Linus along with other pending fixes tonight. It will *not* eliminate the (very real) deadlock. It might make the warning go away, but only if read() on hugetlbfs files doesn't happen during boot. I suspect that they right thing would be to have a way to set explicit nesting rules, not tied to speficic call trace. I hadn't looked into lockdep guts, so no idea how much will that hurt to implement. As in lockdep_lock_nests(class_outer, class_inner, message), acting as if there had been a call chain where class_outer had been taken before class_inner, with message going in place of call trace for that chain when we run into a conflict... -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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>