Re: [PATCH 0/5] fs/buffer: strack reduction on async read

Luis Chamberlain
2024-12-19T02:27:37Z

On Wed, Dec 18, 2024 at 08:05:29PM +0000, Matthew Wilcox wrote:
> On Tue, Dec 17, 2024 at 06:26:21PM -0800, Luis Chamberlain wrote:
> > This splits up a minor enhancement from the bs > ps device support
> > series into its own series for better review / focus / testing.
> > This series just addresses the reducing the array size used and cleaning
> > up the async read to be easier to read and maintain.
>
> How about this approach instead -- get rid of the batch entirely?

Less is more! I wish it worked, but we end up with a null pointer on
ext4/032 (and indeed this is the test that helped me find most bugs in
what I was working on):

[ 105.942462] loop0: detected capacity change from 0 to 1342177280
[ 106.034851] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 106.036903] #PF: supervisor read access in kernel mode
[ 106.038366] #PF: error_code(0x0000) - not-present page
[ 106.039819] PGD 0 P4D 0
[ 106.040574] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
[ 106.041967] CPU: 2 UID: 0 PID: 29 Comm: ksoftirqd/2 Not tainted 6.13.0-rc3+ #42
[ 106.044018] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 2024.08-1 09/18/2024
[ 106.046300] RIP: 0010:end_buffer_async_read_io+0x11/0x90
[ 106.047819] Code: f2 ff 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 53 48 8b 47 10 48 89 fb 48 8b 40 18 <48> 8b 00 f6 40 0d 40 74 0d 0f b7 00 66 25 00 f0 66 3d 00 80 74 09
[ 106.053016] RSP: 0018:ffffa85880137dd0 EFLAGS: 00010246
[ 106.054499] RAX: 0000000000000000 RBX: ffff95e38f22e5b0 RCX: ffff95e39c8753e0
[ 106.056507] RDX: ffff95e3809f8000 RSI: 0000000000000001 RDI: ffff95e38f22e5b0
[ 106.058530] RBP: 0000000000000400 R08: ffff95e3a326b040 R09: 0000000000000001
[ 106.060546] R10: ffffffffbb6070c0 R11: 00000000002dc6c0 R12: 0000000000000000
[ 106.062426] R13: ffff95e3960ea800 R14: ffff95e39586ae40 R15: 0000000000000400
[ 106.064223] FS: 0000000000000000(0000) GS:ffff95e3fbc80000(0000) knlGS:0000000000000000
[ 106.066155] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 106.067473] CR2: 0000000000000000 CR3: 00000001226e2006 CR4: 0000000000772ef0
[ 106.069085] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 106.070571] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 106.072050] PKRU: 55555554
[ 106.072632] Call Trace:
[ 106.073176] <TASK>
[ 106.073611] ? __die_body.cold+0x19/0x26
[ 106.074383] ? page_fault_oops+0xa2/0x230
[ 106.075155] ? __smp_call_single_queue+0xa7/0x110
[ 106.076077] ? do_user_addr_fault+0x63/0x640
[ 106.076916] ? exc_page_fault+0x7a/0x190
[ 106.077639] ? asm_exc_page_fault+0x22/0x30
[ 106.078394] ? end_buffer_async_read_io+0x11/0x90
[ 106.079245] end_bio_bh_io_sync+0x23/0x40
[ 106.079973] blk_update_request+0x178/0x420
[ 106.080727] ? finish_task_switch.isra.0+0x94/0x290
[ 106.081600] blk_mq_end_request+0x18/0x30
[ 106.082281] blk_complete_reqs+0x3d/0x50
[ 106.082954] handle_softirqs+0xf9/0x2c0
[ 106.083607] ? __pfx_smpboot_thread_fn+0x10/0x10
[ 106.084393] run_ksoftirqd+0x37/0x50
[ 106.085012] smpboot_thread_fn+0x184/0x220
[ 106.085688] kthread+0xda/0x110
[ 106.086208] ? __pfx_kthread+0x10/0x10
[ 106.086824] ret_from_fork+0x2d/0x50
[ 106.087409] ? __pfx_kthread+0x10/0x10
[ 106.088013] ret_from_fork_asm+0x1a/0x30
[ 106.088658] </TASK>
[ 106.089045] Modules linked in: loop sunrpc 9p nls_iso8859_1 nls_cp437 vfat fat kvm_intel kvm crct10dif_pclmul ghash_clmulni_intel sha512_ssse3 sha512_generic sha256_ssse3 sha1_ssse3 aesni_intel gf128mul crypto_simd cryptd virtio_balloon 9pnet_virtio virtio_console joydev button evdev serio_raw nvme_fabrics nvme_core dm_mod drm nfnetlink vsock_loopback vmw_vsock_virtio_transport_common vsock autofs4 ext4 crc16 mbcache jbd2 btrfs blake2b_generic efivarfs raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c crc32c_generic raid1 raid0 md_mod virtio_net net_failover virtio_blk failover crc32_pclmul crc32c_intel psmouse virtio_pci virtio_pci_legacy_dev virtio_pci_modern_dev virtio virtio_ring
[ 106.097895] CR2: 0000000000000000
[ 106.098326] ---[ end trace 0000000000000000 ]---

Luis