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When performing the following command in a Xen VM the call trace below is generated.

sudo fstrim -v /

Xen VM host: Xen 4.14.0

Xen Dom0: Linux 4.19.14

Xen DomX: Linux 5.10.6

The code in the kernel triggering this trace is the following.

/* In case the discard granularity isn't set by buggy device driver */
if (WARN_ON_ONCE(!q->limits.discard_granularity)) {
char dev_name[BDEVNAME_SIZE];

bdevname(bdev, dev_name);
pr_err_ratelimited("%s: Error: discard_granularity is 0.\n", dev_name);
return -EOPNOTSUPP;
}

The call trace in the Xen VM.

[ 145.295257] ------------[ cut here ]------------
[ 145.295274] WARNING: CPU: 1 PID: 1230 at block/blk-lib.c:51 __blkdev_issue_discard+0x245/0x2a0
[ 145.295277] Modules linked in: intel_rapl_msr intel_rapl_common crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel crypto_simd cryptd glue_helper rapl joydev bochs_drm drm_vram_helper drm_ttm_helper mousedev xen_kbdfront ttm drm_kms_helper cec syscopyarea sysfillrect sysimgblt xen_netfront fb_sys_fops intel_agp pcspkr intel_gtt mac_hid fuse drm agpgart bpf_preload ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2 ata_generic pata_acpi floppy xen_blkfront crc32c_intel serio_raw ata_piix
[ 145.295373] CPU: 1 PID: 1230 Comm: fstrim Not tainted 5.10.6-arch1-1 #1
[ 145.295376] Hardware name: Xen HVM domU, BIOS 4.14.0 11/14/2020
[ 145.295383] RIP: 0010:__blkdev_issue_discard+0x245/0x2a0
[ 145.295390] Code: 48 8b 44 24 48 65 48 2b 04 25 28 00 00 00 75 6c 8b 44 24 1c 48 83 c4 50 5b 5d 41 5c 41 5d 41 5e 41 5f c3 0f 0b e9 f9 fe ff ff <0f> 0b 48 8d 74 24 28 4c 89 ef e8 ac c2 00 00 48 c7 c6 e0 a1 86 b6
[ 145.295393] RSP: 0018:ffffb283007b7b70 EFLAGS: 00010246
[ 145.295399] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000c40
[ 145.295402] RDX: 00000000000000c0 RSI: 0000000000012240 RDI: ffff8e4980411380
[ 145.295404] RBP: 00000000000000c0 R08: 0000000000000000 R09: ffffb283007b7bf8
[ 145.295407] R10: 0000000000000001 R11: 0000000000002000 R12: 0000000000012240
[ 145.295410] R13: ffff8e4980411380 R14: ffff8e4983b14770 R15: 0000000000000000
[ 145.295415] FS: 00007fd5189fc580(0000) GS:ffff8e498ad00000(0000) knlGS:0000000000000000
[ 145.295418] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 145.295421] CR2: 00005562e06d6448 CR3: 0000000108188001 CR4: 00000000003706e0
[ 145.295432] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 145.295435] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 145.295437] Call Trace:
[ 145.295452] blkdev_issue_discard+0x86/0xe0
[ 145.295510] ext4_trim_fs+0x518/0x930 [ext4]
[ 145.295521] ? mntput_no_expire+0x4a/0x260
[ 145.295568] __ext4_ioctl+0xfee/0x1b10 [ext4]
[ 145.295619] ext4_ioctl+0x2a/0x40 [ext4]
[ 145.295626] __x64_sys_ioctl+0x83/0xb0
[ 145.295634] do_syscall_64+0x33/0x40
[ 145.295640] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 145.295646] RIP: 0033:0x7fd518b71f6b
[ 145.295652] Code: 89 d8 49 8d 3c 1c 48 f7 d8 49 39 c4 72 b5 e8 1c ff ff ff 85 c0 78 ba 4c 89 e0 5b 5d 41 5c c3 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d d5 ae 0c 00 f7 d8 64 89 01 48
[ 145.295655] RSP: 002b:00007ffea645a438 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[ 145.295660] RAX: ffffffffffffffda RBX: 00007ffea645a510 RCX: 00007fd518b71f6b
[ 145.295662] RDX: 00007ffea645a450 RSI: 00000000c0185879 RDI: 0000000000000003
[ 145.295665] RBP: 00005562e06d5440 R08: 00005562e06d5440 R09: 00007ffea645ae87
[ 145.295668] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
[ 145.295670] R13: 00007ffea645ae86 R14: 0000000000000000 R15: ffffffff00000000
[ 145.295677] ---[ end trace 5fcef9628995f731 ]---
[ 145.295682] xvda1: Error: discard_granularity is 0.
[ 145.295703] xvda1: Error: discard_granularity is 0.

Please note that the VM is using a RAW partition as a disk on the VM host.

Attachments: xen-dmesg, dom0-dmesg, domx-dmesg, domx-libvirt-xml are attached.

Arthur Borsboom

Xen VM call trace on fstrim: Error: discard_granularity is 0.