Re: spontaneous crash with "ext4: move ext4 bmap to use iomap infrastructure"

From: Ritesh Harjani
Date: Wed Apr 01 2020 - 10:41:56 EST

Hello Qian,

Thanks for reporting it. By any chance is it your custom kernel.
Any more details on the reproducer & your setup pls.


On 4/1/20 6:08 PM, Qian Cai wrote:
It is not always reproducible so far, but it start to show up on todayâs linux-next. Look
Trough the commits and noticed this recent one matched the new call traces,

ac58e4fb03f9 (âext4: move ext4 bmap to use iomap infrastructure")

Thought?

[ 206.744625][T13224] LTP: starting fallocate04
[ 207.601583][T27684] /dev/zero: Can't open blockdev
[ 208.674301][T27684] EXT4-fs (loop0): mounting ext3 file system using the ext4 subsystem
[ 208.680347][T27684] BUG: Unable to handle kernel instruction fetch (NULL pointer?)
[ 208.680383][T27684] Faulting instruction address: 0x00000000

From above two lines this looks like some NULL function ptr was called.
That's why NIP is 0x0.

But LR shown is ext4_iomap_end(). Now, There is nothing in
ext4_iomap_end() which could cause this. It should just simply return
0 in case of iomap_bmap(). In that function (shown below) flags argument
is 0.

<Code snip>
============
static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length,
ssize_t written, unsigned flags, struct iomap *iomap)
{
/*
* Check to see whether an error occurred while writing out the data to
* the allocated blocks. If so, return the magic error code so that we
* fallback to buffered I/O and attempt to complete the remainder of
* the I/O. Any blocks that may have been allocated in preparation for
* the direct I/O will be reused during buffered I/O.
*/
if (flags & (IOMAP_WRITE | IOMAP_DIRECT) && written == 0)
return -ENOTBLK;

return 0; // ==> should simply return from here.
}

<Tried on my setup>
====================
I did try to mount/unmount on my setup with loop0 and mounting ext3
filesystem using ext4 subsystem. It's working fine as expected.
Here are the tracing logs. Couldn't see any crash.


<LOGS> `(cat trace_pipe |grep iomap_bmap)`
======
<...>-6370 [008] .... 2524.120361: iomap_apply: dev 7:0 ino 0x8 pos 0 length 65536 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
<...>-6380 [010] .... 2526.230331: iomap_apply: dev 7:0 ino 0x8 pos 0 length 1024 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
mount-6389 [010] .... 2528.200383: iomap_apply: dev 7:0 ino 0x8 pos 0 length 4096 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
mount-6398 [010] .... 2530.950352: iomap_apply: dev 7:0 ino 0x8 pos 0 length 65536 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
jbd2/loop0-8-6399 [023] .... 2531.958913: iomap_apply: dev 7:0 ino 0x8 pos 65536 length 65536 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
jbd2/loop0-8-6399 [023] .... 2531.958930: iomap_apply: dev 7:0 ino 0x8 pos 131072 length 65536 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
jbd2/loop0-8-6399 [023] .... 2531.959001: iomap_apply: dev 7:0 ino 0x8 pos 196608 length 65536 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
<...>-6407 [010] .... 2532.960326: iomap_apply: dev 7:0 ino 0x8 pos 0 length 1024 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor
jbd2/loop0-8-6408 [023] .... 2540.010046: iomap_apply: dev 7:0 ino 0x8 pos 1024 length 1024 flags (0x0) ops ext4_iomap_ops [ext4] caller iomap_bmap+0xb0/0xe0 actor iomap_bmap_actor


[ 208.680406][T27684] Oops: Kernel access of bad area, sig: 11 [#1]
[ 208.680439][T27684] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=256 DEBUG_PAGEALLOC NUMA PowerNV
[ 208.680474][T27684] Modules linked in: ext4 crc16 mbcache jbd2 loop kvm_hv kvm ip_tables x_tables xfs sd_mod bnx2x ahci libahci mdio tg3 libata libphy firmware_class dm_mirror dm_region_hash dm_log dm_mod
[ 208.680576][T27684] CPU: 117 PID: 27684 Comm: fallocate04 Tainted: G W 5.6.0-next-20200401+ #288
[ 208.680614][T27684] NIP: 0000000000000000 LR: c0080000102c0048 CTR: 0000000000000000
[ 208.680657][T27684] REGS: c000200361def420 TRAP: 0400 Tainted: G W (5.6.0-next-20200401+)
[ 208.680700][T27684] MSR: 900000004280b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 42022228 XER: 20040000
[ 208.680760][T27684] CFAR: c00800001032c494 IRQMASK: 0
[ 208.680760][T27684] GPR00: c0000000005ac3f8 c000200361def6b0 c00000000165c200 c00020107dae0bd0
[ 208.680760][T27684] GPR04: 0000000000000000 0000000000000400 0000000000000000 0000000000000000
[ 208.680760][T27684] GPR08: c000200361def6e8 c0080000102c0040 000000007fffffff c000000001614e80
[ 208.680760][T27684] GPR12: 0000000000000000 c000201fff671280 0000000000000000 0000000000000002
[ 208.680760][T27684] GPR16: 0000000000000002 0000000000040001 c00020030f5a1000 c00020030f5a1548
[ 208.680760][T27684] GPR20: c0000000015fbad8 c00000000168c654 c000200361def818 c0000000005b4c10
[ 208.680760][T27684] GPR24: 0000000000000000 c0080000103365b8 c00020107dae0bd0 0000000000000400
[ 208.680760][T27684] GPR28: c00000000168c3a8 0000000000000000 0000000000000000 0000000000000000
[ 208.681014][T27684] NIP [0000000000000000] 0x0
[ 208.681065][T27684] LR [c0080000102c0048] ext4_iomap_end+0x8/0x30 [ext4]
[ 208.681091][T27684] Call Trace:
[ 208.681129][T27684] [c000200361def6b0] [c0000000005ac3bc] iomap_apply+0x20c/0x920 (unreliable)
iomap_apply at fs/iomap/apply.c:80 (discriminator 4)
[ 208.681173][T27684] [c000200361def7f0] [c0000000005b4adc] iomap_bmap+0xfc/0x160
iomap_bmap at fs/iomap/fiemap.c:142
[ 208.681228][T27684] [c000200361def850] [c0080000102c2c1c] ext4_bmap+0xa4/0x180 [ext4]
ext4_bmap at fs/ext4/inode.c:3213
[ 208.681260][T27684] [c000200361def890] [c0000000004f71fc] bmap+0x4c/0x80
[ 208.681281][T27684] [c000200361def8c0] [c00800000fdb0acc] jbd2_journal_init_inode+0x44/0x1a0 [jbd2]
jbd2_journal_init_inode at fs/jbd2/journal.c:1255
[ 208.681326][T27684] [c000200361def960] [c00800001031c808] ext4_load_journal+0x440/0x860 [ext4]
[ 208.681371][T27684] [c000200361defa30] [c008000010322a14] ext4_fill_super+0x342c/0x3ab0 [ext4]
[ 208.681414][T27684] [c000200361defba0] [c0000000004cb0bc] mount_bdev+0x25c/0x290
[ 208.681478][T27684] [c000200361defc40] [c008000010310250] ext4_mount+0x28/0x50 [ext4]
[ 208.681520][T27684] [c000200361defc60] [c00000000053242c] legacy_get_tree+0x4c/0xb0
[ 208.681556][T27684] [c000200361defc90] [c0000000004c864c] vfs_get_tree+0x4c/0x130
[ 208.681593][T27684] [c000200361defd00] [c00000000050a1c8] do_mount+0xa18/0xc50
[ 208.681641][T27684] [c000200361defdd0] [c00000000050a9a8] sys_mount+0x158/0x180
[ 208.681679][T27684] [c000200361defe20] [c00000000000b3f8] system_call+0x5c/0x68
[ 208.681726][T27684] Instruction dump:
[ 208.681747][T27684] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
[ 208.681797][T27684] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
[ 208.681839][T27684] ---[ end trace 4e9e2bab7f1d4048 ]---
[ 208.802259][T27684]
[ 209.802373][T27684] Kernel panic - not syncing: Fatal exception


Others,
Any clue here?


After this I am definitely setting up full LTP suite too at my end.
I mostly was using xfstests for my testing.


-ritesh