Re: [3.18rc1] btrfs triggering vm bug_on
From: Robert White
Date: Tue Oct 21 2014 - 22:03:47 EST
It _looks_ like a hard out-of-ram event and not necessarily a filesystem
implementation problem.
One of the systems I work with has zero swap but still allows overcommit
in the VM. It would do things like this all the time back in development
(and I suspect it still does but the developers got rid of those pesky
logs). Not necessarily this exact error, but lots of them with the same
"feel".
You are actually triggering two bugs, only the second being in btrfs code.
The VM_BUG_ON_PAGE() in cleancache_get_page() (mm/cleancache.c) is going
off first. This is presumably the ram exhaustion event, which is an
outer problem taking place in your system (e.g. the real cause).
This floats back to the __do_readpage() which doesn't (and almost
cannot) figure out how the page validation failed
if (!PageUptodate(page)) {
if (cleancache_get_page(page) == 0) {
BUG_ON(blocksize != PAGE_SIZE);
unlock_extent(tree, start, end);
goto out;
}
}
Which (improperly) ends with this suspect bit from the out: in
__do_readpage() where the unlock_page() is called unconditionally.
out:
if (!nr) {
if (!PageError(page))
SetPageUptodate(page);
unlock_page(page);
}
I _think_ the call to unlock_page() _should_ have an if
(PageLocked(page)) in front of it.
--- extent_io.c 2014-09-19 03:26:21.058266026 -0700
+++ extent_io.c 2014-10-21 18:52:45.127713115 -0700
@@ -2960,7 +2960,8 @@
if (!nr) {
if (!PageError(page))
SetPageUptodate(page);
- unlock_page(page);
+ if (PageLocked(page))
+ unlock_page(page);
}
return 0;
}
That said, the question of what your system is going to do with the VM
memory exhausted is a bigger problem.
-- Rob.
On 10/21/2014 05:50 PM, Qu Wenruo wrote:
Any reproducer?
Thanks,
Qu
-------- Original Message --------
Subject: [3.18rc1] btrfs triggering vm bug_on
From: Dave Jones <davej@xxxxxxxxxx>
To: Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>
Date: 2014å10æ22æ 05:57
page:ffffea00088aa1c0 count:4 mapcount:0 mapping:ffff88009901e2d8
index:0x0
flags: 0x2ffc0000000806(error|referenced|private)
page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
------------[ cut here ]------------
kernel BUG at mm/filemap.c:747!
invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
Modules linked in: fuse snd_seq_dummy tun binfmt_misc usb_debug bnep
rfcomm nfnetlink scsi_transport_iscsi hidp af_key llc2 can_bcm can_raw
nfc caif_socket caif
af_802154 ieee802154 phonet af_rxrpc bluetooth can pppoe pppox
ppp_generic slhc irda crc_ccitt rds rose sctp libcrc32c x25 atm netrom
appletalk ipx p8023 psnap p8022 llc ax25 c
fg80211 rfkill btrfs xor coretemp hwmon x86_pkg_temp_thermal kvm_intel
snd_hda_codec_realtek snd_hda_codec_generic snd_hda_codec_hdmi kvm
snd_hda_intel snd_hda_controller snd_h
da_codec snd_hwdep crct10dif_pclmul snd_seq crc32c_intel
ghash_clmulni_intel e1000e snd_seq_device raid6_pq snd_pcm microcode
snd_timer serio_raw snd pcspkr ptp pps_core shpchp
soundcore nfsd auth_rpcgss oid_registry nfs_acl lockd grace sunrpc
CPU: 3 PID: 6466 Comm: trinity-c402 Not tainted 3.18.0-rc1+ #72
task: ffff88003ec22f00 ti: ffff88006f3ac000 task.ti: ffff88006f3ac000
RIP: 0010:[<ffffffffbb1a06df>] [<ffffffffbb1a06df>]
unlock_page+0x7f/0x90
RSP: 0018:ffff88006f3afa08 EFLAGS: 00010292
RAX: 0000000000000036 RBX: 0000000000001000 RCX: 0000000000000006
RDX: 0000000000000000 RSI: ffffffffbb843c53 RDI: ffffffffbb0e399e
RBP: ffff88006f3afa08 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000c2b
R13: 0000000000000000 R14: ffffea00088aa1c0 R15: 0000000000000000
FS: 00007f7e30942740(0000) GS:ffff880244e00000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7e2d8b8000 CR3: 0000000098e56000 CR4: 00000000001407e0
DR0: 000000000219e000 DR1: 0000000000de8000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
ffff88006f3afb28 ffffffffc05adf78 ffffffffc05ae375 ffff88006f3afa70
ffffffffbb03d193 ffffffffbb0b25c5 ffffffffc05adb10 0000000000000000
00000000211ce98b 0000000000000000 ffff88006f3afbd0 ffff880222a87000
Call Trace:
[<ffffffffc05adf78>] __do_readpage+0x468/0x7a0 [btrfs]
[<ffffffffc05ae375>] ? __extent_read_full_page+0xc5/0xe0 [btrfs]
[<ffffffffbb03d193>] ? prepare_ftrace_return+0x73/0xe0
[<ffffffffbb0b25c5>] ? preempt_count_sub+0x5/0x100
[<ffffffffc05adb10>] ?
extent_write_cache_pages.isra.30.constprop.48+0x440/0x440 [btrfs]
[<ffffffffc0590290>] ? btrfs_writepage_end_io_hook+0x360/0x360 [btrfs]
[<ffffffffbb0b263b>] ? preempt_count_sub+0x7b/0x100
[<ffffffffbb8567ba>] ? ftrace_graph_caller+0x5a/0x85
[<ffffffffc05ae375>] __extent_read_full_page+0xc5/0xe0 [btrfs]
[<ffffffffc0590290>] ? btrfs_writepage_end_io_hook+0x360/0x360 [btrfs]
[<ffffffffbb8567ba>] ? ftrace_graph_caller+0x5a/0x85
[<ffffffffc05af426>] extent_read_full_page+0x46/0x80 [btrfs]
[<ffffffffc058d265>] btrfs_readpage+0x25/0x30 [btrfs]
[<ffffffffc059da78>] prepare_uptodate_page+0x38/0xa0 [btrfs]
[<ffffffffc059dbec>] prepare_pages.isra.19+0x10c/0x1a0 [btrfs]
[<ffffffffc059ed54>] __btrfs_buffered_write+0x1e4/0x5f0 [btrfs]
[<ffffffffbb8567ba>] ? ftrace_graph_caller+0x5a/0x85
[<ffffffffc059f52e>] btrfs_file_write_iter+0x3ce/0x550 [btrfs]
[<ffffffffbb341060>] ? cap_inode_getsecid+0x20/0x20
[<ffffffffbb21aad0>] ? new_sync_read+0xd0/0xd0
[<ffffffffbb21ab5e>] new_sync_write+0x8e/0xd0
[<ffffffffbb8567ba>] ? ftrace_graph_caller+0x5a/0x85
[<ffffffffbb21b53a>] vfs_write+0xba/0x1f0
[<ffffffffbb21c048>] SyS_write+0x58/0xd0
[<ffffffffbb854689>] tracesys_phase2+0xd4/0xd9
Code: 48 8d 0c 92 48 8d 0c 4a 48 8b 96 98 00 00 00 48 89 c6 48 8d 3c
ca 31 d2 e8 df d5 f2 ff 5d c3 48 c7 c6 38 81 c7 bb e8 01 ff 02 00 <0f>
0b 66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 e8 6b 60 6b
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