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. -- 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>