[PATCH] ocfs2: fix crash caused by stale lvb with fsdlm plugin

From: Eric Ren
Date: Fri Dec 09 2016 - 04:31:39 EST

The crash happens rather often when we reset some cluster
nodes while nodes contend fiercely to do truncate and append.

The crash backtrace is below:
"
[ 245.197849] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover_grant 1 locks on 971 resources
[ 245.197859] dlm: C21CBDA5E0774F4BA5A9D4F317717495: dlm_recover 9 generation 5 done: 4 ms
[ 245.198379] ocfs2: Begin replay journal (node 318952601, slot 2) on device (253,18)
[ 247.272338] ocfs2: End replay journal (node 318952601, slot 2) on device (253,18)
[ 247.547084] ocfs2: Beginning quota recovery on device (253,18) for slot 2
[ 247.683263] ocfs2: Finishing quota recovery on device (253,18) for slot 2
[ 247.833022] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: bug expression: le64_to_cpu(fe->i_size) != i_size_read(inode)
[ 247.833029] (truncate,30154,1):ocfs2_truncate_file:470 ERROR: Inode 290321, inode i_size = 732 != di i_size = 937, i_flags = 0x1
[ 247.833074] ------------[ cut here ]------------
[ 247.833077] kernel BUG at /usr/src/linux/fs/ocfs2/file.c:470!
[ 247.833079] invalid opcode: 0000 [#1] SMP
[ 247.833081] Modules linked in: ocfs2_stack_user(OEN) ocfs2(OEN) ocfs2_nodemanager ocfs2_stackglue(OEN) quota_tree dlm(OEN) configfs fuse sd_mod iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi af_packet iscsi_ibft iscsi_boot_sysfs softdog xfs libcrc32c ppdev parport_pc pcspkr parport joydev virtio_balloon virtio_net i2c_piix4 acpi_cpufreq button processor ext4 crc16 jbd2 mbcache ata_generic cirrus virtio_blk ata_piix drm_kms_helper ahci syscopyarea libahci sysfillrect sysimgblt fb_sys_fops ttm floppy libata drm virtio_pci virtio_ring uhci_hcd virtio ehci_hcd usbcore serio_raw usb_common sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua scsi_mod autofs4
[ 247.833107] Supported: No, Unsupported modules are loaded
[ 247.833110] CPU: 1 PID: 30154 Comm: truncate Tainted: G OE N 4.4.21-69-default #1
[ 247.833111] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20151112_172657-sheep25 04/01/2014
[ 247.833112] task: ffff88004ff6d240 ti: ffff880074e68000 task.ti: ffff880074e68000
[ 247.833113] RIP: 0010:[<ffffffffa05c8c30>] [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
[ 247.833151] RSP: 0018:ffff880074e6bd50 EFLAGS: 00010282
[ 247.833152] RAX: 0000000000000074 RBX: 000000000000029e RCX: 0000000000000000
[ 247.833153] RDX: 0000000000000001 RSI: 0000000000000246 RDI: 0000000000000246
[ 247.833154] RBP: ffff880074e6bda8 R08: 000000003675dc7a R09: ffffffff82013414
[ 247.833155] R10: 0000000000034c50 R11: 0000000000000000 R12: ffff88003aab3448
[ 247.833156] R13: 00000000000002dc R14: 0000000000046e11 R15: 0000000000000020
[ 247.833157] FS: 00007f839f965700(0000) GS:ffff88007fc80000(0000) knlGS:0000000000000000
[ 247.833158] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 247.833159] CR2: 00007f839f97e000 CR3: 0000000036723000 CR4: 00000000000006e0
[ 247.833164] Stack:
[ 247.833165] 00000000000003a9 0000000000000001 ffff880060554000 ffff88004fcaf000
[ 247.833167] ffff88003aa7b090 1000000000000000 ffff88003aab3448 ffff880074e6beb0
[ 247.833169] 0000000000000001 0000000000002068 0000000000000020 0000000000000000
[ 247.833171] Call Trace:
[ 247.833208] [<ffffffffa05cb1a8>] ocfs2_setattr+0x698/0xa90 [ocfs2]
[ 247.833225] [<ffffffff8121587e>] notify_change+0x1ae/0x380
[ 247.833242] [<ffffffff811f8bfe>] do_truncate+0x5e/0x90
[ 247.833246] [<ffffffff811f8f58>] do_sys_ftruncate.constprop.11+0x108/0x160
[ 247.833257] [<ffffffff815e142e>] entry_SYSCALL_64_fastpath+0x12/0x6d
[ 247.834724] DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x6d
[ 247.834725]
[ 247.834726] Leftover inexact backtrace:

[ 247.834728] Code: 24 28 ba d6 01 00 00 48 c7 c6 30 43 62 a0 8b 41 2c 89 44 24 08 48 8b 41 20 48 c7 c1 78 a3 62 a0 48 89 04 24 31 c0 e8 a0 97 f9 ff <0f> 0b 3d 00 fe ff ff 0f 84 ab fd ff ff 83 f8 fc 0f 84 a2 fd ff
[ 247.834748] RIP [<ffffffffa05c8c30>] ocfs2_truncate_file+0x640/0x6c0 [ocfs2]
[ 247.834774] RSP <ffff880074e6bd50>
"

It's because ocfs2_inode_lock() get us stale LVB in which the i_size is not
equal to the disk i_size. We mistakenly trust the LVB because the underlaying
fsdlm dlm_lock() doesn't set lkb_sbflags with DLM_SBF_VALNOTVALID properly for
us. But, why?

The current code tries to downconvert lock without DLM_LKF_VALBLK
flag to tell o2cb don't update RSB's LVB if it's a PR->NULL conversion,
even if the lock resource type needs LVB. This is not the right way for fsdlm.

The fsdlm plugin behaves different on DLM_LKF_VALBLK, it depends on
DLM_LKF_VALBLK to decide if we care about the LVB in the LKB. If DLM_LKF_VALBLK
is not set, fsdlm will skip recovering RSB's LVB from this lkb and set the right
DLM_SBF_VALNOTVALID appropriately when node failure happens.

The following diagram briefly illustrates how this crash happens:

RSB1 is inode metadata lock resource with LOCK_TYPE_USES_LVB;

The 1st round:

Node1 Node2
RSB1: PR
RSB1(master): NULL->EX
ocfs2_downconvert_lock(PR->NULL, set_lvb==0)
ocfs2_dlm_lock(no DLM_LKF_VALBLK)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

dlm_lock(no DLM_LKF_VALBLK)
convert_lock(overwrite lkb->lkb_exflags
with no DLM_LKF_VALBLK)

RSB1: NULL RSB1: EX
reset Node2
dlm_recover_rsbs()
recover_lvb()

/* The LVB is not trustable if the node with EX fails and
* no lock >= PR is left. We should set RSB_VALNOTVALID for RSB1.
*/

if(!(kb_exflags & DLM_LKF_VALBLK)) /* This means we miss the chance to
return; * to invalid the LVB here.
*/

The 2nd round:

Node 1 Node2
RSB1(become master from recovery)

ocfs2_setattr()
ocfs2_inode_lock(NULL->EX)
/* dlm_lock() return the stale lvb without setting DLM_SBF_VALNOTVALID */
ocfs2_meta_lvb_is_trustable() return 1 /* so we don't refresh inode from disk */
ocfs2_truncate_file()
mlog_bug_on_msg(disk isize != i_size_read(inode)) /* crash! */

The fix is quite straightforward. We keep to set DLM_LKF_VALBLK flag for dlm_lock()
if the lock resource type needs LVB and the fsdlm plugin is uesed.

Signed-off-by: Eric Ren <zren@xxxxxxxx>
---
fs/ocfs2/dlmglue.c | 10 ++++++++++
fs/ocfs2/stackglue.c | 6 ++++++
fs/ocfs2/stackglue.h | 3 +++
3 files changed, 19 insertions(+)

diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 83d576f..77d1632 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -3303,6 +3303,16 @@ static int ocfs2_downconvert_lock(struct ocfs2_super *osb,
mlog(ML_BASTS, "lockres %s, level %d => %d\n", lockres->l_name,
lockres->l_level, new_level);

+ /*
+ * On DLM_LKF_VALBLK, fsdlm behaves differently with o2cb. It always
+ * expects DLM_LKF_VALBLK being set if the LKB has LVB, so that
+ * we can recover correctly from node failure. Otherwise, we may get
+ * invalid LVB in LKB, but without DLM_SBF_VALNOTVALID being set.
+ */
+ if (!ocfs2_is_o2cb_active() &&
+ lockres->l_ops->flags & LOCK_TYPE_USES_LVB)
+ lvb = 1;
+
if (lvb)
dlm_flags |= DLM_LKF_VALBLK;

diff --git a/fs/ocfs2/stackglue.c b/fs/ocfs2/stackglue.c
index 52c07346b..8203590 100644
--- a/fs/ocfs2/stackglue.c
+++ b/fs/ocfs2/stackglue.c
@@ -48,6 +48,12 @@ static char ocfs2_hb_ctl_path[OCFS2_MAX_HB_CTL_PATH] = "/sbin/ocfs2_hb_ctl";
*/
static struct ocfs2_stack_plugin *active_stack;

+inline int ocfs2_is_o2cb_active(void)
+{
+ return !strcmp(active_stack->sp_name, OCFS2_STACK_PLUGIN_O2CB);
+}
+EXPORT_SYMBOL_GPL(ocfs2_is_o2cb_active);
+
static struct ocfs2_stack_plugin *ocfs2_stack_lookup(const char *name)
{
struct ocfs2_stack_plugin *p;
diff --git a/fs/ocfs2/stackglue.h b/fs/ocfs2/stackglue.h
index f2dce10..e3036e1 100644
--- a/fs/ocfs2/stackglue.h
+++ b/fs/ocfs2/stackglue.h
@@ -298,6 +298,9 @@ void ocfs2_stack_glue_set_max_proto_version(struct ocfs2_protocol_version *max_p
int ocfs2_stack_glue_register(struct ocfs2_stack_plugin *plugin);
void ocfs2_stack_glue_unregister(struct ocfs2_stack_plugin *plugin);

+/* In ocfs2_downconvert_lock(), we need to know which stack we are using */
+int ocfs2_is_o2cb_active(void);
+
extern struct kset *ocfs2_kset;

#endif /* STACKGLUE_H */
--
2.6.6