Commit [c48a11c7: netvm: propagate page->pfmemalloc to skb] is responsible for the following bug triggered by a xen network driver [ 1.908592] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010 [ 1.908643] IP: [<ffffffffa0037750>] xennet_poll+0x980/0xec0 [xen_netfront] [ 1.908703] PGD ea1df067 PUD e8ada067 PMD 0 [ 1.908774] Oops: 0000 [#1] SMP [ 1.908797] Modules linked in: fbcon tileblit font radeon bitblit softcursor ttm drm_kms_helper crc32c_intel xen_blkfront xen_netfront xen_fbfront fb_sys_fops sysimgblt sysfillrect syscopyarea +xen_kbdfront xenfs xen_privcmd [ 1.908938] CPU 0 [ 1.908950] Pid: 2165, comm: ip Not tainted 3.5.0upstream-08854-g444fa66 #1 [ 1.908983] RIP: e030:[<ffffffffa0037750>] [<ffffffffa0037750>] xennet_poll+0x980/0xec0 [xen_netfront] [ 1.909029] RSP: e02b:ffff8800ffc03db8 EFLAGS: 00010282 [ 1.909055] RAX: ffff8800ea010140 RBX: ffff8800f00e86c0 RCX: 000000000000009a [ 1.909055] RDX: 0000000000000040 RSI: 000000000000005a RDI: ffff8800fa7dee80 [ 1.909055] RBP: ffff8800ffc03ee8 R08: ffff8800f00e86d8 R09: ffff8800ea010000 [ 1.909055] R10: dead000000200200 R11: dead000000100100 R12: ffff8800fa7dee80 [ 1.909055] R13: 000000000000005a R14: ffff8800fa7dee80 R15: 0000000000000200 [ 1.909055] FS: 00007fbafc188700(0000) GS:ffff8800ffc00000(0000) knlGS:0000000000000000 [ 1.909055] CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b [ 1.909055] CR2: 0000000000000010 CR3: 00000000ea108000 CR4: 0000000000002660 [ 1.909055] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 1.909055] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 [ 1.909055] Process ip (pid: 2165, threadinfo ffff8800ea0f2000, task ffff8800fa783040) [ 1.909055] Stack: [ 1.909055] ffff8800e27e5040 ffff8800ffc03e88 ffff8800ffc03e68 ffff8800ffc03e48 [ 1.909055] 7fffffffffffffff ffff8800ffc03e00 ffff8800e27e5040 ffff8800f00e86d8 [ 1.909055] ffff8800ffc03eb0 00000040ffffffff ffff8800f00e8000 00000000ffc03e30 [ 1.909055] Call Trace: [ 1.909055] <IRQ> [ 1.909055] [<ffffffff81066028>] ? pvclock_clocksource_read+0x58/0xd0 [ 1.909055] [<ffffffff81486352>] net_rx_action+0x112/0x240 [ 1.909055] [<ffffffff8107f319>] __do_softirq+0xb9/0x190 [ 1.909055] [<ffffffff815d8d7c>] call_softirq+0x1c/0x30 The problem is that the xenfront driver is passing a NULL page to __skb_fill_page_desc() which was unexpected. This patch checks that there is a page before dereferencing. Reported-and-Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> Signed-off-by: Mel Gorman <mgorman@xxxxxxx> --- include/linux/skbuff.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 7632c87..8857669 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1256,7 +1256,7 @@ static inline void __skb_fill_page_desc(struct sk_buff *skb, int i, * do not lose pfmemalloc information as the pages would not be * allocated using __GFP_MEMALLOC. */ - if (page->pfmemalloc && !page->mapping) + if (page && page->pfmemalloc && !page->mapping) skb->pfmemalloc = true; frag->page.p = page; frag->page_offset = off; -- 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>