NULL pointer exception in btrfs_compress_pages

NULL pointer exception in btrfs_compress_pages

[Marc Lehmann]

Hi!

It seems some kernel newer than 5.4.55 has introduced a NULL pointer
access in btrfs_compress_pages.

5.4.45 and 5.4.55 work fine on the systems in question, while 5.4.73 and
5.8.17 both generate variations of the following oops at some point during
runtime (usually within 1-2 hours, sometimes at boot). btrfs scrub and
btrfsck find nothing to complain about in the filesystems, and compression
is not globally enabled on the filesystems (but possibly enabled for some
directories).

[ 2735.988544] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 2735.996149] #PF: supervisor instruction fetch in kernel mode
[ 2736.003692] #PF: error_code(0x0010) - not-present page
[ 2736.011098] PGD 0 P4D 0 
[ 2736.018429] Oops: 0010 [#1] SMP NOPTI
[ 2736.025643] CPU: 3 PID: 6853 Comm: kworker/u8:9 Not tainted 5.4.73-050473-generic #202010291054
[ 2736.032992] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./C2550D4I, BIOS P2.30 01/26/2016
[ 2736.047966] Workqueue: btrfs-delalloc btrfs_work_helper [btrfs]
[ 2736.055481] RIP: 0010:0x0
[ 2736.062828] Code: Bad RIP value.
[ 2736.070001] RSP: 0018:ffffafafc389fce8 EFLAGS: 00010282
[ 2736.077117] RAX: 0000000000000000 RBX: ffffffffc0595a60 RCX: ffff8a2995282250
[ 2736.084345] RDX: 00000000000fc000 RSI: ffff8a29a192ec98 RDI: ffff8a2a623e37e0
[ 2736.091651] RBP: ffffafafc389fd30 R08: ffffafafc389fda0 R09: ffffafafc389fdb0
[ 2736.098860] R10: ffff8a2a623e37e0 R11: ffff8a2995282250 R12: ffff8a2a623e37e0
[ 2736.105936] R13: ffff8a29a192ec98 R14: 00000000000fc000 R15: ffff8a2995282250
[ 2736.113016] FS:  0000000000000000(0000) GS:ffff8a2a6fb80000(0000) knlGS:0000000000000000
[ 2736.120108] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2736.127049] CR2: ffffffffffffffd6 CR3: 000000026d40a000 CR4: 00000000001006e0
[ 2736.133957] Call Trace:
[ 2736.140687]  btrfs_compress_pages+0x6b/0xa0 [btrfs]
[ 2736.147444]  compress_file_range+0x2e2/0x830 [btrfs]
[ 2736.154301]  ? submit_compressed_extents+0x430/0x430 [btrfs]
[ 2736.161085]  async_cow_start+0x16/0x40 [btrfs]
[ 2736.167715]  btrfs_work_helper+0xc1/0x3a0 [btrfs]
[ 2736.174166]  ? __schedule+0x2eb/0x740
[ 2736.180473]  process_one_work+0x1eb/0x3b0
[ 2736.186761]  worker_thread+0x4d/0x400
[ 2736.192888]  kthread+0x104/0x140
[ 2736.198819]  ? process_one_work+0x3b0/0x3b0
[ 2736.204741]  ? kthread_park+0x90/0x90
[ 2736.210660]  ret_from_fork+0x1f/0x40
[ 2736.216421] Modules linked in: xfs dm_crypt msr bfq intel_powerclamp kvm_intel kvm crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel snd_pcm crypto_simd snd_timer cryptd glue_helper intel_cstate snd soundcore joydev pcspkr input_leds ipmi_ssif mac_hid ipmi_si ipmi_devintf ipmi_msghandler nct6775 hwmon_vid coretemp sunrpc ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear ses enclosure hid_generic usbkbd usbmouse usbhid hid gpio_ich i2c_ismt mpt3sas lpc_ich igb i2c_i801 i2c_algo_bit ahci dca raid_class libahci scsi_transport_sas
[ 2736.258562] CR2: 0000000000000000
[ 2736.264814] ---[ end trace 696b8659e073a6a0 ]---
[ 2736.295596] RIP: 0010:0x0
[ 2736.301519] Code: Bad RIP value.
[ 2736.307333] RSP: 0018:ffffafafc389fce8 EFLAGS: 00010282
[ 2736.313169] RAX: 0000000000000000 RBX: ffffffffc0595a60 RCX: ffff8a2995282250
[ 2736.319087] RDX: 00000000000fc000 RSI: ffff8a29a192ec98 RDI: ffff8a2a623e37e0
[ 2736.325030] RBP: ffffafafc389fd30 R08: ffffafafc389fda0 R09: ffffafafc389fdb0
[ 2736.330974] R10: ffff8a2a623e37e0 R11: ffff8a2995282250 R12: ffff8a2a623e37e0
[ 2736.336873] R13: ffff8a29a192ec98 R14: 00000000000fc000 R15: ffff8a2995282250
[ 2736.342795] FS:  0000000000000000(0000) GS:ffff8a2a6fb80000(0000) knlGS:0000000000000000
[ 2736.348832] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2736.354847] CR2: ffffffffffffffd6 CR3: 000000026d40a000 CR4: 00000000001006e0


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