From b520252aa287b14e1f39a51e20051775b273b82a Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 22 Jan 2015 08:13:17 -0700 Subject: [PATCH] fs: make inode_to_bdi() handle NULL inode Running a heavy fs workload, I ran into a situation where we pass down a page for writeback/swap that doesn't have an inode mapping: BUG: unable to handle kernel NULL pointer dereference at 0000000000000028 IP: [] inode_to_bdi+0xf/0x50 PGD 0 Oops: 0000 [#1] PREEMPT SMP Modules linked in: wl(O) tun cfg80211 btusb joydev hid_apple hid_generic usbhid hid bcm5974 usb_storage nouveau snd_hda_codec_hdmi snd_hda_codec_cirrus snd_hda_codec_generic x86_pkg_temp_thermal snd_hda_intel kvm_intel snd_hda_controller snd_hda_codec kvm snd_hwdep snd_pcm applesmc input_polldev snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_timer snd_seq_device snd xhci_pci xhci_hcd ttm thunderbolt soundcore apple_gmux apple_bl bluetooth binfmt_misc fuse nls_iso8859_1 nls_cp437 vfat fat [last unloaded: wl] CPU: 4 PID: 50 Comm: kswapd0 Tainted: G U O 3.19.0-rc5+ #60 Hardware name: Apple Inc. MacBookPro11,3/Mac-2BD1B31983FE1663, BIOS MBP112.88Z.0138.B02.1310181745 10/18/2013 task: ffff880462e917f0 ti: ffff880462edc000 task.ti: ffff880462edc000 RIP: 0010:[] [] inode_to_bdi+0xf/0x50 RSP: 0000:ffff880462edf8e8 EFLAGS: 00010282 RAX: ffffffff81c4cd80 RBX: ffffea0001b3abc0 RCX: 0000000000000000 RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffff880462edf8f8 R08: 00000000001e8500 R09: ffff880460f7cb68 R10: ffff880462edfa00 R11: 0000000000000101 R12: 0000000000000000 R13: ffffffff81c4cd98 R14: 0000000000000000 R15: ffff880460f7c9c0 FS: 0000000000000000(0000) GS:ffff88047f300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000028 CR3: 00000002b6341000 CR4: 00000000001407e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: ffffea0001b3abc0 ffffffff81c4cd80 ffff880462edf948 ffffffff811244aa ffffffff811565b0 ffff880460f7c9c0 ffff880462edf948 ffffea0001b3abc0 0000000000000001 ffff880462edfb40 ffff880008b999c0 ffff880460f7c9c0 Call Trace: [] __test_set_page_writeback+0x3a/0x170 [] ? SyS_madvise+0x790/0x790 [] __swap_writepage+0x216/0x280 [] ? radix_tree_insert+0x32/0xe0 [] ? swap_info_get+0x61/0xf0 [] ? page_swapcount+0x4c/0x60 [] swap_writepage+0x2d/0x50 [] shmem_writepage+0x198/0x2c0 [] shrink_page_list+0x464/0xa00 [] shrink_inactive_list+0x266/0x500 [] shrink_lruvec+0x5d5/0x720 [] shrink_zone+0x5b/0x190 [] kswapd+0x48f/0x8d0 [] ? try_to_free_pages+0x4c0/0x4c0 [] kthread+0xd2/0xf0 [] ? workqueue_congested+0x30/0x80 [] ? kthread_create_on_node+0x180/0x180 [] ret_from_fork+0x7c/0xb0 [] ? kthread_create_on_node+0x180/0x180 Code: 00 48 c7 c7 8d 8d a4 81 e8 3f 62 eb ff e9 fc fe ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41 54 49 89 fc 53 <48> 8b 5f 28 48 89 df e8 15 f8 00 00 85 c0 75 11 48 8b 83 d8 00 RIP [] inode_to_bdi+0xf/0x50 RSP CR2: 0000000000000028 ---[ end trace eb0e21aa7dad3ddf ]--- Handle this in inode_to_bdi() by punting it to noop_backing_dev_info, if mapping->host is NULL. Signed-off-by: Jens Axboe --- fs/fs-writeback.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index a20b1145f4d5..c399152de397 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -68,7 +68,12 @@ EXPORT_SYMBOL(writeback_in_progress); struct backing_dev_info *inode_to_bdi(struct inode *inode) { - struct super_block *sb = inode->i_sb; + struct super_block *sb; + + if (!inode) + return &noop_backing_dev_info; + + sb = inode->i_sb; #ifdef CONFIG_BLOCK if (sb_is_blkdev_sb(sb)) return blk_get_backing_dev_info(I_BDEV(inode)); -- 2.39.5