On Thu, Oct 30, 2014 at 10:24:47AM -0400, Sasha Levin wrote: > On 10/30/2014 10:14 AM, Johannes Weiner wrote: > >> The problem is that you are attempting to read 'locked' when you call > >> > mem_cgroup_end_page_stat(), so it gets used even before you enter the > >> > function - and using uninitialized variables is undefined. > > We are not using that value anywhere if !memcg. What path are you > > referring to? > > You're using that value as soon as you are passing it to a function, it > doesn't matter what happens inside that function. It's copied as part of the pass-by-value protocol, but we really don't do anything with it. So why does it matter? > >> > Yes, it's a compiler warning. > > Could you provide that please, including arch, and gcc version? > > On x86, > > $ gcc --version > gcc (GCC) 5.0.0 20141029 (experimental) > > [ 26.868116] ================================================================================ > [ 26.870376] UBSan: Undefined behaviour in mm/rmap.c:1084:2 Well, "compiler warning" is misleading at best, this is some out-of-tree runtime debugging tool. As per above, there isn't a practical problem here, but your patch worsens the code by making callsites ignorant of how the interface works. -- 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>