On Sat, May 13, 2017 at 03:10:40PM +0200, Andrea Arcangeli wrote: > "err" needs to be left set to -EFAULT if split_huge_page > succeeds. Otherwise if "err" gets clobbered with zero and > write_protect_page fails, try_to_merge_one_page() will succeed instead > of returning -EFAULT and then try_to_merge_with_ksm_page() will > continue thinking kpage is a PageKsm when in fact it's still an > anonymous page. Eventually it'll crash in page_add_anon_rmap. > > This has been reproduced on Fedora25 kernel but I can reproduce with > upstream too. > > The bug was introduced in commit > f765f540598a129dc4bb6f698fd4acc92f296c14 in v4.5. > > page:fffff67546ce1cc0 count:4 mapcount:2 mapping:ffffa094551e36e1 index:0x7f0f46673 > flags: 0x2ffffc0004007c(referenced|uptodate|dirty|lru|active|swapbacked) > page dumped because: VM_BUG_ON_PAGE(!PageLocked(page)) > page->mem_cgroup:ffffa09674bf0000 > ------------[ cut here ]------------ > kernel BUG at mm/rmap.c:1222! > invalid opcode: 0000 [#1] SMP > CPU: 1 PID: 76 Comm: ksmd Not tainted 4.9.3-200.fc25.x86_64 #1 > task: ffffa0968be65b80 task.stack: ffffc0e941b3c000 > RIP: 0010:[<ffffffff9a20ac94>] [<ffffffff9a20ac94>] do_page_add_anon_rmap+0x1c4/0x240 > RSP: 0018:ffffc0e941b3fd48 EFLAGS: 00010282 > RAX: 0000000000000021 RBX: fffff67546ce1cc0 RCX: 0000000000000006 > RDX: 0000000000000000 RSI: 0000000000000246 RDI: ffffa0969ec4e0a0 > RBP: ffffc0e941b3fd70 R08: 0000000000018a84 R09: 0000000000000005 > R10: fffff6754f87de00 R11: 000000000000049f R12: 00007fe6f5f67000 > R13: ffffa094990ecc00 R14: 0000000000000000 R15: ffffa093c369c480 > FS: 0000000000000000(0000) GS:ffffa0969ec40000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f4c21c221f0 CR3: 0000000152e07000 CR4: 00000000000426e0 > Stack: > fffff675470fd9c0 00007fe6f5f67000 fffff67540f8a900 ffffa094990ecc00 > ffffa093c369c480 ffffc0e941b3fd80 ffffffff9a20ad28 ffffc0e941b3fe00 > ffffffff9a228b4b 80000001c3f67807 0000000000000000 80000001c3f67805 > Call Trace: > [<ffffffff9a20ad28>] page_add_anon_rmap+0x18/0x20 > [<ffffffff9a228b4b>] try_to_merge_with_ksm_page+0x50b/0x780 > [<ffffffff9a229fd1>] ksm_scan_thread+0x1211/0x1410 > [<ffffffff9a0e7270>] ? prepare_to_wait_event+0x100/0x100 > [<ffffffff9a228dc0>] ? try_to_merge_with_ksm_page+0x780/0x780 > [<ffffffff9a0c2569>] kthread+0xd9/0xf0 > [<ffffffff9a0c2490>] ? kthread_park+0x60/0x60 > [<ffffffff9a81be55>] ret_from_fork+0x25/0x30 > > Reported-by: Federico Simoncelli <fsimonce@xxxxxxxxxx> > Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> -- Kirill A. Shutemov -- 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>
