On Wed, 26 Mar 2014, Sasha Levin wrote: > Hi all, > > While fuzzing with trinity inside a KVM tools guest running the latest -next > kernel I've stumbled on the following. > > Out of curiosity, is there a reason not to do bad flag checks when actually > setting flag? Obviously it'll be slower but it'll be easier catching these > issues.o I don't see how it would help here. > > [ 3926.683948] BUG: Bad page state in process ksmd pfn:5a6246 > [ 3926.689336] page:ffffea0016989180 count:0 mapcount:0 mapping: > (null) index: > [ 3926.696507] page flags: > 0x56fffff8028001c(referenced|uptodate|dirty|swapbacked|mlock > [ 3926.709201] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set > [ 3926.711216] bad because of flags: > [ 3926.712136] page flags: 0x200000(mlocked) > [ 3926.713574] Modules linked in: > [ 3926.714466] CPU: 26 PID: 3864 Comm: ksmd Tainted: G W > 3.14.0-rc7-next-201 > [ 3926.720942] ffffffff85688060 ffff8806ec7abc38 ffffffff844bd702 > 0000000000002fa0 > [ 3926.728107] ffffea0016989180 ffff8806ec7abc68 ffffffff844b158f > 000fffff80000000 > [ 3926.730563] 0000000000000000 000fffff80000000 ffffffff85688060 > ffff8806ec7abcb8 > [ 3926.737653] Call Trace: > [ 3926.738347] dump_stack (lib/dump_stack.c:52) > [ 3926.739841] bad_page (arch/x86/include/asm/atomic.h:38 > include/linux/mm.h:432 mm/page_alloc.c:339) > [ 3926.741296] free_pages_prepare (mm/page_alloc.c:644 mm/page_alloc.c:738) > [ 3926.742818] free_hot_cold_page (mm/page_alloc.c:1371) > [ 3926.749425] __put_single_page (mm/swap.c:71) > [ 3926.751074] put_page (mm/swap.c:237) > [ 3926.752398] ksm_do_scan (mm/ksm.c:1480 mm/ksm.c:1704) > [ 3926.753957] ksm_scan_thread (mm/ksm.c:1723) > [ 3926.755940] ? bit_waitqueue (kernel/sched/wait.c:291) > [ 3926.758644] ? ksm_do_scan (mm/ksm.c:1715) > [ 3926.760420] kthread (kernel/kthread.c:219) > [ 3926.761605] ? kthread_create_on_node (kernel/kthread.c:185) > [ 3926.763149] ret_from_fork (arch/x86/kernel/entry_64.S:555) > [ 3926.764323] ? kthread_create_on_node (kernel/kthread.c:185) I've thought about this some, and slept on it, but don't yet see how it comes about. I'll have to come back to it later. Was it a one-off, or do you find it fairly easy to reproduce? If the latter, it would be interesting to know if it comes from recent changes or not. mm/mlock.c does appear to have been under continuous revision for several releases (but barely changed in next). Thanks, Hugh -- 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>