On Thu, 23 May 2013, Peter Zijlstra wrote: > On Thu, May 23, 2013 at 10:10:36AM -0400, Vince Weaver wrote: > > > > I can confirm your patch avoids the oops on my machine. > > > > It does lead to interesting behavior if I run the sample program > > multiple times (with added printfs): > > > > vince@core2:~$ ./perf_mmap_close_bug > > mmap1=0x7f06a6e90000 > > mmap2=0x7f06a6e7f000 > > vince@core2:~$ ./perf_mmap_close_bug > > mmap1=0x7f878a138000 > > mmap2=0x7f878a127000 > > vince@core2:~$ ./perf_mmap_close_bug > > mmap1=0xffffffffffffffff > > Error opening fd2 Invalid argument > > > > and then it never successfully completes again. Is this unexpected > > behavior? > > Sounds weird to me, I'll see if I can reproduce/understand. I tracked this down in case you haven't already. The problem is that in the kernel patched with your patch locked_vm is getting decremented twice in the sample code and going negative. I'm not sure why this isn't a problem until the third time through. Here are my crude debug printk results from kernel/events/core.c [ 28.684862] user_extra: 17 user_lock_limit: 129 [ 28.698458] user_locked: 17 locked_vm: 0 user_extra 17 [ 28.713853] locked: 0 locked_vm: 0 pinned_vm: 0 extra: 0 lock_limit: 16 [ 28.733728] perf_mmap: locked_vm: 17 [ 28.744509] mmap_close: locked_vm=0 [ 28.754939] mmap_close: locked_vm=-17 [ 29.472741] user_extra: 17 user_lock_limit: 129 [ 29.486332] user_locked: 0 locked_vm: -17 user_extra 17 [ 29.501996] locked: 0 locked_vm: 0 pinned_vm: 0 extra: 0 lock_limit: 16 [ 29.521874] perf_mmap: locked_vm: 0 [ 29.532400] mmap_close: locked_vm=-17 [ 29.543352] mmap_close: locked_vm=-34 [ 30.028236] user_extra: 17 user_lock_limit: 129 [ 30.041835] user_locked: -17 locked_vm: -34 user_extra 17 [ 30.058018] extra: -275 user_locked: -17 user_lock_limit: 258 [ 30.075232] locked: -275 locked_vm: 0 pinned_vm: 0 extra: -275 lock_limit: 16 Vince -- To unsubscribe from this list: send the line "unsubscribe trinity" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
