Date: Tue, 28 May 2024 10:42:16 +0200
From: Friedrich Weber <f.weber@...xmox.com>
To: Chengming Zhou <chengming.zhou@...ux.dev>, axboe@...nel.dk,
 ming.lei@...hat.com, hch@....de, bvanassche@....org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 zhouchengming@...edance.com
Subject: Re: [PATCH v4 4/4] blk-flush: reuse rq queuelist in flush state
 machine

Hi Chengming,

Thanks again!

On 28/05/2024 02:12, Chengming Zhou wrote:
> Another possibility is that drivers may change rq->queuelist even after
> rq->end_io(). So add two more BUG_ON() to detect this:
> 
> diff --git a/block/blk-flush.c b/block/blk-flush.c
> index e73dc22d05c1..0eb684a468e5 100644
> --- a/block/blk-flush.c
> +++ b/block/blk-flush.c
> @@ -179,7 +179,10 @@ static void blk_flush_complete_seq(struct request *rq,
> 
>         switch (seq) {
>         case REQ_FSEQ_PREFLUSH:
> +               BUG_ON(rq->queuelist.next == NULL);
> +               fallthrough;
>         case REQ_FSEQ_POSTFLUSH:
> +               BUG_ON(rq->queuelist.next == NULL);
>                 /* queue for flush */
>                 if (list_empty(pending))
>                         fq->flush_pending_since = jiffies;
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index d98654869615..908fdfb62132 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2963,6 +2963,8 @@ void blk_mq_submit_bio(struct bio *bio)
>                         return;
>         }
> 
> +       BUG_ON(rq->queuelist.next == NULL);
> +
>         trace_block_getrq(bio);
> 
>         rq_qos_track(q, rq, bio);
> @@ -2977,6 +2979,8 @@ void blk_mq_submit_bio(struct bio *bio)
>                 return;
>         }
> 
> +       BUG_ON(rq->queuelist.next == NULL);
> +
>         if (op_is_flush(bio->bi_opf) && blk_insert_flush(rq))
>                 return;
> 

I applied the following patch (with slightly different line numbers) to
my checkout of Linux 6.9:

diff --git a/block/blk-flush.c b/block/blk-flush.c
index b0f314f4bc14..07e0de3b28ef 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -179,7 +179,10 @@ static void blk_flush_complete_seq(struct request *rq,

        switch (seq) {
        case REQ_FSEQ_PREFLUSH:
+               BUG_ON(rq->queuelist.next == NULL);
+               fallthrough;
        case REQ_FSEQ_POSTFLUSH:
+               BUG_ON(rq->queuelist.next == NULL);
                /* queue for flush */
                if (list_empty(pending))
                        fq->flush_pending_since = jiffies;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 32afb87efbd0..13a8f4dd1e5b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2988,6 +2988,8 @@ void blk_mq_submit_bio(struct bio *bio)
                blk_mq_use_cached_rq(rq, plug, bio);
        }

+       BUG_ON(rq->queuelist.next == NULL);
+
        trace_block_getrq(bio);

        rq_qos_track(q, rq, bio);
@@ -3002,6 +3004,8 @@ void blk_mq_submit_bio(struct bio *bio)
                return;
        }

+       BUG_ON(rq->queuelist.next == NULL);
+
        if (op_is_flush(bio->bi_opf) && blk_insert_flush(rq))
                return;

Hope I did this correctly. With this, the reproducer triggered a BUG
pretty quickly, see [0]. If I can provide anything else, just let me know.

I forgot to mention earlier that I'm running the reproducer against a
QEMU/KVM guest too, for convenience -- so, the "host" from my previous
post is in fact running virtualized. I don't think it should be relevant
here, but I'll try to run the reproducer against real hardware too.

Best,

Friedrich

[0]

[   37.543834] kernel BUG at block/blk-mq.c:2991!
[   37.544458] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[   37.545077] CPU: 4 PID: 795 Comm: kvm Tainted: G            E
6.9.0-troubleshoot1-dirty #28
[   37.546087] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   37.547389] RIP: 0010:blk_mq_submit_bio+0x6f5/0x750
[   37.547949] Code: ff e9 aa fc ff ff e8 7a 3c a4 ff 48 89 de 4c 89 e7
e8 9f ef ff ff e8 da 79 a4 ff e9 99 fc ff ff e8 d0 45 a7 ff e9 cd fa ff
ff <0f> 0b 0f 0b 48 8b 03 48 8b 40 68 48 8b 40 40 e9 8c fb ff ff f6 43
[   37.550088] RSP: 0018:ffffa2b480863a70 EFLAGS: 00010246
[   37.550685] RAX: 0000000000000000 RBX: ffff971c0b29d000 RCX:
0000000000000000
[   37.551502] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
0000000000000000
[   37.552325] RBP: ffffa2b480863ae8 R08: 0000000000000000 R09:
0000000000000000
[   37.553130] R10: 0000000000000000 R11: 0000000000000000 R12:
ffff971c106ee600
[   37.553934] R13: ffff971c0fb328f0 R14: ffff971c03b330c0 R15:
0000000000000001
[   37.554747] FS:  00007bcc47e006c0(0000) GS:ffff971d37c00000(0000)
knlGS:0000000000000000
[   37.555663] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   37.556311] CR2: 000070d06e1a40a0 CR3: 000000010b6f4004 CR4:
0000000000372ef0
[   37.557117] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[   37.557935] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[   37.558789] Call Trace:
[   37.559080]  <TASK>
[   37.559355]  ? show_regs+0x6c/0x80
[   37.560276]  ? die+0x37/0xa0
[   37.560633]  ? do_trap+0xda/0xf0
[   37.561023]  ? do_error_trap+0x71/0xb0
[   37.561486]  ? blk_mq_submit_bio+0x6f5/0x750
[   37.562008]  ? exc_invalid_op+0x52/0x80
[   37.562463]  ? blk_mq_submit_bio+0x6f5/0x750
[   37.562987]  ? asm_exc_invalid_op+0x1b/0x20
[   37.563492]  ? blk_mq_submit_bio+0x6f5/0x750
[   37.564007]  __submit_bio+0xb3/0x1c0
[   37.564439]  submit_bio_noacct_nocheck+0x2fc/0x3d0
[   37.565019]  submit_bio_noacct+0x1ba/0x6b0
[   37.565508]  flush_bio_list+0x71/0x110 [raid1]
[   37.566049]  raid1_unplug+0x3c/0xf0 [raid1]
[   37.566539]  __blk_flush_plug+0xbe/0x140
[   37.567016]  blk_finish_plug+0x30/0x50
[   37.567466]  io_submit_sqes+0x4c4/0x6c0
[   37.567942]  ? syscall_exit_to_user_mode+0x81/0x270
[   37.568530]  __do_sys_io_uring_enter+0x2f2/0x640
[   37.569070]  __x64_sys_io_uring_enter+0x22/0x40
[   37.569626]  x64_sys_call+0x20b9/0x24b0
[   37.570071]  do_syscall_64+0x80/0x170
[   37.570525]  ? vfs_read+0x240/0x380
[   37.570937]  ? ksys_read+0xe6/0x100
[   37.571360]  ? syscall_exit_to_user_mode+0x81/0x270
[   37.571930]  ? do_syscall_64+0x8c/0x170
[   37.572402]  ? syscall_exit_to_user_mode+0x81/0x270
[   37.572969]  ? do_syscall_64+0x8c/0x170
[   37.573438]  ? irqentry_exit+0x43/0x50
[   37.573878]  ? clear_bhb_loop+0x15/0x70
[   37.574348]  ? clear_bhb_loop+0x15/0x70
[   37.574806]  ? clear_bhb_loop+0x15/0x70
[   37.575282]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[   37.575891] RIP: 0033:0x7bcc58f45b95
[   37.576335] Code: 00 00 00 44 89 d0 41 b9 08 00 00 00 83 c8 10 f6 87
d0 00 00 00 01 8b bf cc 00 00 00 44 0f 45 d0 45 31 c0 b8 aa 01 00 00 0f
05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 41 83 e2 02 74 c2 f0 48 83 0c 24
[   37.578468] RSP: 002b:00007bcc47dfafd8 EFLAGS: 00000246 ORIG_RAX:
00000000000001aa
[   37.579359] RAX: ffffffffffffffda RBX: 00007bcc400039d0 RCX:
00007bcc58f45b95
[   37.580198] RDX: 0000000000000000 RSI: 0000000000000003 RDI:
0000000000000033
[   37.581028] RBP: 00007bcc400039d8 R08: 0000000000000000 R09:
0000000000000008
[   37.581864] R10: 0000000000000000 R11: 0000000000000246 R12:
00007bcc40003ac0
[   37.582695] R13: 0000000000000000 R14: 0000591ad05f5c68 R15:
0000591b10198450
[   37.583534]  </TASK>
[   37.583812] Modules linked in: veth(E) cmac(E) nls_utf8(E) cifs(E)
cifs_arc4(E) nls_ucs2_utils(E) rdma_cm(E) iw_cm(E) ib_cm(E) ib_core(E)
cifs_md4(E) netfs(E) ebtable_filter(E) ebtables(E) ip_set(E)
ip6table_raw(E) iptable_raw(E) ip6table_filter(E) ip6_tables(E)
iptable_filter(E) nf_tables(E) softdog(E) sunrpc(E) binfmt_misc(E)
bonding(E) tls(E) nfnetlink_log(E) nfnetlink(E) intel_rapl_msr(E)
intel_rapl_common(E) intel_uncore_frequency_common(E) intel_pmc_core(E)
intel_vsec(E) pmt_telemetry(E) pmt_class(E) kvm_intel(E) kvm(E)
crct10dif_pclmul(E) polyval_clmulni(E) polyval_generic(E)
ghash_clmulni_intel(E) sha256_ssse3(E) sha1_ssse3(E) hid_generic(E)
aesni_intel(E) crypto_simd(E) cryptd(E) usbhid(E) hid(E) rapl(E)
pcspkr(E) vmgenid(E) joydev(E) input_leds(E) mac_hid(E) serio_raw(E)
vhost_net(E) vhost(E) vhost_iotlb(E) tap(E) efi_pstore(E) dmi_sysfs(E)
qemu_fw_cfg(E) ip_tables(E) x_tables(E) autofs4(E) raid10(E) raid456(E)
async_raid6_recov(E) async_memcpy(E) async_pq(E) async_xor(E)
async_tx(E) xor(E) raid6_pq(E)
[   37.583875]  libcrc32c(E) raid0(E) raid1(E) crc32_pclmul(E)
psmouse(E) bochs(E) drm_vram_helper(E) drm_ttm_helper(E) uhci_hcd(E)
ttm(E) ehci_hcd(E) i2c_piix4(E) pata_acpi(E) floppy(E)
[   37.595967] ---[ end trace 0000000000000000 ]---
[   37.596555] RIP: 0010:blk_mq_submit_bio+0x6f5/0x750
[   37.597144] Code: ff e9 aa fc ff ff e8 7a 3c a4 ff 48 89 de 4c 89 e7
e8 9f ef ff ff e8 da 79 a4 ff e9 99 fc ff ff e8 d0 45 a7 ff e9 cd fa ff
ff <0f> 0b 0f 0b 48 8b 03 48 8b 40 68 48 8b 40 40 e9 8c fb ff ff f6 43
[   37.599320] RSP: 0018:ffffa2b480863a70 EFLAGS: 00010246
[   37.599932] RAX: 0000000000000000 RBX: ffff971c0b29d000 RCX:
0000000000000000
[   37.600757] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
0000000000000000
[   37.601600] RBP: ffffa2b480863ae8 R08: 0000000000000000 R09:
0000000000000000
[   37.602450] R10: 0000000000000000 R11: 0000000000000000 R12:
ffff971c106ee600
[   37.603299] R13: ffff971c0fb328f0 R14: ffff971c03b330c0 R15:
0000000000000001
[   37.604129] FS:  00007bcc47e006c0(0000) GS:ffff971d37c00000(0000)
knlGS:0000000000000000
[   37.605079] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   37.605774] CR2: 000070d06e1a40a0 CR3: 000000010b6f4004 CR4:
0000000000372ef0
[   37.606620] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[   37.607464] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[   37.608335] ------------[ cut here ]------------
[   37.608885] WARNING: CPU: 4 PID: 795 at kernel/exit.c:827
do_exit+0x8a2/0xab0
[   37.609754] Modules linked in: veth(E) cmac(E) nls_utf8(E) cifs(E)
cifs_arc4(E) nls_ucs2_utils(E) rdma_cm(E) iw_cm(E) ib_cm(E) ib_core(E)
cifs_md4(E) netfs(E) ebtable_filter(E) ebtables(E) ip_set(E)
ip6table_raw(E) iptable_raw(E) ip6table_filter(E) ip6_tables(E)
iptable_filter(E) nf_tables(E) softdog(E) sunrpc(E) binfmt_misc(E)
bonding(E) tls(E) nfnetlink_log(E) nfnetlink(E) intel_rapl_msr(E)
intel_rapl_common(E) intel_uncore_frequency_common(E) intel_pmc_core(E)
intel_vsec(E) pmt_telemetry(E) pmt_class(E) kvm_intel(E) kvm(E)
crct10dif_pclmul(E) polyval_clmulni(E) polyval_generic(E)
ghash_clmulni_intel(E) sha256_ssse3(E) sha1_ssse3(E) hid_generic(E)
aesni_intel(E) crypto_simd(E) cryptd(E) usbhid(E) hid(E) rapl(E)
pcspkr(E) vmgenid(E) joydev(E) input_leds(E) mac_hid(E) serio_raw(E)
vhost_net(E) vhost(E) vhost_iotlb(E) tap(E) efi_pstore(E) dmi_sysfs(E)
qemu_fw_cfg(E) ip_tables(E) x_tables(E) autofs4(E) raid10(E) raid456(E)
async_raid6_recov(E) async_memcpy(E) async_pq(E) async_xor(E)
async_tx(E) xor(E) raid6_pq(E)
[   37.609827]  libcrc32c(E) raid0(E) raid1(E) crc32_pclmul(E)
psmouse(E) bochs(E) drm_vram_helper(E) drm_ttm_helper(E) uhci_hcd(E)
ttm(E) ehci_hcd(E) i2c_piix4(E) pata_acpi(E) floppy(E)
[   37.622013] CPU: 4 PID: 795 Comm: kvm Tainted: G      D     E
6.9.0-troubleshoot1-dirty #28
[   37.623045] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   37.624382] RIP: 0010:do_exit+0x8a2/0xab0
[   37.624869] Code: 38 0c 00 00 e9 2d fe ff ff 49 8d 7d 18 e8 b6 83 07
00 e9 5a f8 ff ff 48 8b bb f8 09 00 00 31 f6 e8 b3 e0 ff ff e9 c1 fd ff
ff <0f> 0b e9 d4 f7 ff ff 0f 0b e9 8f f7 ff ff 4c 89 e6 bf 05 06 00 00
[   37.627117] RSP: 0018:ffffa2b480863ec8 EFLAGS: 00010286
[   37.627780] RAX: 0000000000000000 RBX: ffff971c05458000 RCX:
0000000000000000
[   37.628638] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
0000000000000000
[   37.629512] RBP: ffffa2b480863f20 R08: 0000000000000000 R09:
0000000000000000
[   37.630379] R10: 0000000000000000 R11: 0000000000000000 R12:
000000000000000b
[   37.631231] R13: ffff971c04c8d100 R14: ffff971c00c28000 R15:
ffffa2b4808639c8
[   37.632095] FS:  00007bcc47e006c0(0000) GS:ffff971d37c00000(0000)
knlGS:0000000000000000
[   37.633090] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   37.633794] CR2: 000070d06e1a40a0 CR3: 000000010b6f4004 CR4:
0000000000372ef0
[   37.634666] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[   37.635533] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[   37.636387] Call Trace:
[   37.636692]  <TASK>
[   37.636963]  ? show_regs+0x6c/0x80
[   37.637393]  ? __warn+0x88/0x140
[   37.637801]  ? do_exit+0x8a2/0xab0
[   37.638197]  ? report_bug+0x182/0x1b0
[   37.638674]  ? handle_bug+0x46/0x90
[   37.639094]  ? exc_invalid_op+0x18/0x80
[   37.639577]  ? asm_exc_invalid_op+0x1b/0x20
[   37.640090]  ? do_exit+0x8a2/0xab0
[   37.640537]  ? do_exit+0x6f/0xab0
[   37.640941]  ? syscall_exit_to_user_mode+0x81/0x270
[   37.641542]  make_task_dead+0x81/0x160
[   37.641999]  rewind_stack_and_make_dead+0x16/0x20
[   37.642586] RIP: 0033:0x7bcc58f45b95
[   37.643046] Code: 00 00 00 44 89 d0 41 b9 08 00 00 00 83 c8 10 f6 87
d0 00 00 00 01 8b bf cc 00 00 00 44 0f 45 d0 45 31 c0 b8 aa 01 00 00 0f
05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 41 83 e2 02 74 c2 f0 48 83 0c 24
[   37.645251] RSP: 002b:00007bcc47dfafd8 EFLAGS: 00000246 ORIG_RAX:
00000000000001aa
[   37.646213] RAX: ffffffffffffffda RBX: 00007bcc400039d0 RCX:
00007bcc58f45b95
[   37.647117] RDX: 0000000000000000 RSI: 0000000000000003 RDI:
0000000000000033
[   37.648018] RBP: 00007bcc400039d8 R08: 0000000000000000 R09:
0000000000000008
[   37.648916] R10: 0000000000000000 R11: 0000000000000246 R12:
00007bcc40003ac0
[   37.649824] R13: 0000000000000000 R14: 0000591ad05f5c68 R15:
0000591b10198450
[   37.650760]  </TASK>
[   37.651034] ---[ end trace 0000000000000000 ]---

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