From: Steve Capper <steve.capper@xxxxxxxxxx> Date: Tue, 14 Oct 2014 13:38:34 +0100 > On Mon, Oct 13, 2014 at 12:06:18PM -0400, David Miller wrote: >> From: Steve Capper <steve.capper@xxxxxxxxxx> >> Date: Mon, 13 Oct 2014 12:44:28 +0100 >> >> > Also, as a heads up for Sparc. I don't see any definition of >> > __get_user_pages_fast. Does this mean that a futex on THP tail page >> > can cause an infinite loop? >> >> I have no idea, I didn't realize this was required to be implemented. > > In get_futex_key, a call is made to __get_user_pages_fast to handle the > case where a THP tail page needs to be pinned for the futex. There is a > stock implementation of __get_user_pages_fast, but this is just an > empty function that returns 0. Unfortunately this will provoke a goto > to "again:" and end up in an infinite loop. The process will appear > to hang with a high system cpu usage. I'd rather the build fail and force me to implement the interface for my architecture than have a default implementation that causes issues like that. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>