On Sun, Jan 12, 2014 at 01:25:21AM -0800, Hugh Dickins wrote: > We see General Protection Fault on RSI in copy_page_rep: > that RSI is what you get from a NULL struct page pointer. > > RIP: 0010:[<ffffffff81154955>] [<ffffffff81154955>] copy_page_rep+0x5/0x10 > RSP: 0000:ffff880136e15c00 EFLAGS: 00010286 > RAX: ffff880000000000 RBX: ffff880136e14000 RCX: 0000000000000200 > RDX: 6db6db6db6db6db7 RSI: db73880000000000 RDI: ffff880dd0c00000 > RBP: ffff880136e15c18 R08: 0000000000000200 R09: 000000000005987c > R10: 000000000005987c R11: 0000000000000200 R12: 0000000000000001 > R13: ffffea00305aa000 R14: 0000000000000000 R15: 0000000000000000 > FS: 00007f195752f700(0000) GS:ffff880c7fc20000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000093010000 CR3: 00000001458e1000 CR4: 00000000000027e0 > Call Trace: > [<ffffffff810f2835>] ? copy_user_highpage.isra.43+0x65/0x80 > [<ffffffff812654b2>] copy_user_huge_page+0x93/0xab > [<ffffffff8127cc76>] do_huge_pmd_wp_page+0x710/0x815 > [<ffffffff81055ab8>] handle_mm_fault+0x15d8/0x1d70 > [<ffffffff814f909d>] __do_page_fault+0x14d/0x840 > [<ffffffff810a13ad>] ? SYSC_recvfrom+0x10d/0x210 > [<ffffffff814f97bf>] do_page_fault+0x2f/0x90 > [<ffffffff814f6032>] page_fault+0x22/0x30 > > do_huge_pmd_wp_page() tests is_huge_zero_pmd(orig_pmd) four times: > but since shrink_huge_zero_page() can free the huge_zero_page, and > we have no hold of our own on it here (except where the fourth test > holds page_table_lock and has checked pmd_same), it's possible for > it to answer yes the first time, but no to the second or third test. > Change all those last three to tests for NULL page. > > (Note: this is not the same issue as trinity's DEBUG_PAGEALLOC BUG > in copy_page_rep with RSI: ffff88009c422000, reported by Sasha Levin > in https://lkml.org/lkml/2013/3/29/103. I believe that one is due > to the source page being split, and a tail page freed, while copy > is in progress; and not a problem without DEBUG_PAGEALLOC, since > the pmd_same check will prevent a miscopy from being made visible.) > > Fixes: 97ae17497e99 ("thp: implement refcounting for huge zero page") > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # v3.10 v3.11 v3.12 Reviewed-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>