Re: [PATCH] md/raid10: fix data corruption and crash during resync

[Shaohua Li <shli@kernel.org>]

On Wed, Nov 04, 2015 at 05:30:30PM +0100, Artur Paszkiewicz wrote:
> The commit c31df25f20e3 ("md/raid10: make sync_request_write() call
> bio_copy_data()") replaced manual data copying with bio_copy_data() but
> it doesn't work as intended. The source bio (fbio) is already processed,
> so its bvec_iter has bi_size == 0 and bi_idx == bi_vcnt.  Because of
> this, bio_copy_data() either does not copy anything, or worse, copies
> data from the ->bi_next bio if it is set.  This causes wrong data to be
> written to drives during resync and sometimes lockups/crashes in
> bio_copy_data():
> 
> [  517.338478] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [md126_raid10:3319]
> [  517.347324] Modules linked in: raid10 xt_CHECKSUM ipt_MASQUERADE nf_nat_masquerade_ipv4 tun ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw iptable_filter ip_tables x86_pkg_temp_thermal coretemp kvm_intel kvm crct10dif_pclmul crc32_pclmul cryptd shpchp pcspkr ipmi_si ipmi_msghandler tpm_crb acpi_power_meter acpi_cpufreq ext4 mbcache jbd2 sr_mod cdrom sd_mod e1000e ax88179_178a usbnet mii ahci ata_generic crc32c_intel libahci ptp pata_acpi l
 ibata pps_core wmi sunrpc dm_mirror dm_region_hash dm_log dm_mod
> [  517.440555] CPU: 0 PID: 3319 Comm: md126_raid10 Not tainted 4.3.0-rc6+ #1
> [  517.448384] Hardware name: Intel Corporation PURLEY/PURLEY, BIOS PLYDCRB1.86B.0055.D14.1509221924 09/22/2015
> [  517.459768] task: ffff880153773980 ti: ffff880150df8000 task.ti: ffff880150df8000
> [  517.468529] RIP: 0010:[<ffffffff812e1888>]  [<ffffffff812e1888>] bio_copy_data+0xc8/0x3c0
> [  517.478164] RSP: 0018:ffff880150dfbc98  EFLAGS: 00000246
> [  517.484341] RAX: ffff880169356688 RBX: 0000000000001000 RCX: 0000000000000000
> [  517.492558] RDX: 0000000000000000 RSI: ffffea0001ac2980 RDI: ffffea0000d835c0
> [  517.500773] RBP: ffff880150dfbd08 R08: 0000000000000001 R09: ffff880153773980
> [  517.508987] R10: ffff880169356600 R11: 0000000000001000 R12: 0000000000010000
> [  517.517199] R13: 000000000000e000 R14: 0000000000000000 R15: 0000000000001000
> [  517.525412] FS:  0000000000000000(0000) GS:ffff880174a00000(0000) knlGS:0000000000000000
> [  517.534844] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  517.541507] CR2: 00007f8a044d5fed CR3: 0000000169504000 CR4: 00000000001406f0
> [  517.549722] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [  517.557929] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [  517.566144] Stack:
> [  517.568626]  ffff880174a16bc0 ffff880153773980 ffff880169356600 0000000000000000
> [  517.577659]  0000000000000001 0000000000000001 ffff880153773980 ffff88016a61a800
> [  517.586715]  ffff880150dfbcf8 0000000000000001 ffff88016dd209e0 0000000000001000
> [  517.595773] Call Trace:
> [  517.598747]  [<ffffffffa043ef95>] raid10d+0xfc5/0x1690 [raid10]
> [  517.605610]  [<ffffffff816697ae>] ? __schedule+0x29e/0x8e2
> [  517.611987]  [<ffffffff814ff206>] md_thread+0x106/0x140
> [  517.618072]  [<ffffffff810c1d80>] ? wait_woken+0x80/0x80
> [  517.624252]  [<ffffffff814ff100>] ? super_1_load+0x520/0x520
> [  517.630817]  [<ffffffff8109ef89>] kthread+0xc9/0xe0
> [  517.636506]  [<ffffffff8109eec0>] ? flush_kthread_worker+0x70/0x70
> [  517.643653]  [<ffffffff8166d99f>] ret_from_fork+0x3f/0x70
> [  517.649929]  [<ffffffff8109eec0>] ? flush_kthread_worker+0x70/0x70
> 
> Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
> ---
>  drivers/md/raid10.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 96f3659..23bbe61 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -1944,6 +1944,8 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>  
>  	first = i;
>  	fbio = r10_bio->devs[i].bio;
> +	fbio->bi_iter.bi_size = r10_bio->sectors << 9;
> +	fbio->bi_iter.bi_idx = 0;
>  
>  	vcnt = (r10_bio->sectors + (PAGE_SIZE >> 9) - 1) >> (PAGE_SHIFT - 9);
>  	/* now find blocks with errors */
> @@ -1987,7 +1989,7 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>  		bio_reset(tbio);
>  
>  		tbio->bi_vcnt = vcnt;
> -		tbio->bi_iter.bi_size = r10_bio->sectors << 9;
> +		tbio->bi_iter.bi_size = fbio->bi_iter.bi_size;
>  		tbio->bi_rw = WRITE;
>  		tbio->bi_private = r10_bio;
>  		tbio->bi_iter.bi_sector = r10_bio->devs[i].addr;

Looks good. Reviewed-by: Shaohua Li <shli@kernel.org>

A nitpick, I'm wondering if we should do a full reset like raid1 does to make this more clear.