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Date: Fri, 01 Aug 2014 09:10:10 +0200
From: Juergen Gross <jgross@...e.com>
To: James Bottomley <James.Bottomley@...senPartnership.com>
CC: linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Oops in scsi_put_host_cmd_pool
On 08/01/2014 09:05 AM, James Bottomley wrote:
> On Fri, 2014-08-01 at 08:02 +0200, Juergen Gross wrote:
>> On 08/01/2014 07:41 AM, Juergen Gross wrote:
>>> During test of Xen pvSCSI frontend module I found the following issue:
>>>
>>> When unplugging a passed-through SCSI-device the SCSI Host is removed.
>>> When calling the final scsi_host_put() from the driver an Oops is
>>> happening:
>>>
>>> [ 219.816292] (file=drivers/scsi/xen-scsifront.c, line=808)
>>> scsifront_remove: device/vscsi/1 removed
>>> [ 219.816371] BUG: unable to handle kernel NULL pointer dereference at
>>> 0000000000000010
>>> [ 219.816380] IP: [<ffffffff805fdcf8>] scsi_put_host_cmd_pool+0x38/0xb0
>>> [ 219.816390] PGD 3bd60067 PUD 3d353067 PMD 0
>>> [ 219.816396] Oops: 0000 [#1] SMP
>>> [ 219.816400] Modules linked in: nls_utf8 sr_mod cdrom xen_scsifront
>>> xt_pkttype xt_LOG xt_limit af_packet ip6t_REJECT xt_tcpudp
>>> nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_raw ipt_REJECT iptable_raw
>>> xt_CT iptable_filter ip6table_mangle nf_conntrack_netbios_ns
>>> nf_conntrack_broadcast nf_conntrack_ipv4 nf_defrag_ipv4 ip_tables
>>> xt_conntrack nf_conntrack ip6table_filter ip6_tables x_tables
>>> x86_pkg_temp_thermal thermal_sys coretemp hwmon crc32_pclmul
>>> crc32c_intel ghash_clmulni_intel aesni_intel ablk_helper cryptd lrw
>>> gf128mul glue_helper aes_x86_64 microcode pcspkr sg dm_mod autofs4
>>> scsi_dh_alua scsi_dh_emc scsi_dh_rdac scsi_dh_hp_sw scsi_dh xen_blkfront
>>> xen_netfront
>>> [ 219.816458] CPU: 0 PID: 23 Comm: xenwatch Not tainted
>>> 3.16.0-rc6-11-xen+ #66
>>> [ 219.816463] task: ffff88003da985d0 ti: ffff88003da9c000 task.ti:
>>> ffff88003da9c000
>>> [ 219.816467] RIP: e030:[<ffffffff805fdcf8>] [<ffffffff805fdcf8>]
>>> scsi_put_host_cmd_pool+0x38/0xb0
>>> [ 219.816474] RSP: e02b:ffff88003da9fc20 EFLAGS: 00010202
>>> [ 219.816477] RAX: ffffffffa01a50c0 RBX: 0000000000000000 RCX:
>>> 0000000000000003
>>> [ 219.816481] RDX: 0000000000000240 RSI: ffff88003d242b80 RDI:
>>> ffffffff80c708c0
>>> [ 219.816485] RBP: ffff88003da9fc38 R08: 4f7e974a31ed0290 R09:
>>> 0000000000000000
>>> [ 219.816488] R10: 0000000000007ff0 R11: 0000000000000001 R12:
>>> ffff8800038f8000
>>> [ 219.816491] R13: ffffffffa01a50c0 R14: 0000000000000000 R15:
>>> 0000000000000000
>>> [ 219.816498] FS: 00007fe2e2eeb700(0000) GS:ffff88003f800000(0000)
>>> knlGS:0000000000000000
>>> [ 219.816502] CS: e033 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [ 219.816505] CR2: 0000000000000010 CR3: 000000003d20c000 CR4:
>>> 0000000000042660
>>> [ 219.816509] Stack:
>>> [ 219.816511] ffff8800038f8000 ffff8800038f8030 ffff880003ae3400
>>> ffff88003da9fc58
>>> [ 219.816516] ffffffff805fe78b ffff8800038f8000 ffff88003bb82c40
>>> ffff88003da9fc80
>>> [ 219.816521] ffffffff805ff587 ffff8800038f81a0 ffff8800038f8190
>>> ffff880003ae3400
>>> [ 219.816527] Call Trace:
>>> [ 219.816533] [<ffffffff805fe78b>]
>>> scsi_destroy_command_freelist+0x5b/0x60
>>> [ 219.816538] [<ffffffff805ff587>] scsi_host_dev_release+0x97/0xe0
>>> [ 219.816543] [<ffffffff805dd71d>] device_release+0x2d/0xa0
>>> [ 219.816548] [<ffffffff804dbec7>] kobject_cleanup+0x77/0x1b0
>>> [ 219.816553] [<ffffffff804dbd70>] kobject_put+0x30/0x60
>>> [ 219.816556] [<ffffffff805dd9e2>] put_device+0x12/0x20
>>> [ 219.816560] [<ffffffff805ff490>] scsi_host_put+0x10/0x20
>>> [ 219.816565] [<ffffffffa01a2042>] scsifront_free+0x42/0x90
>>> [xen_scsifront]
>>> [ 219.816569] [<ffffffffa01a20ad>] scsifront_remove+0x1d/0x50
>>> [xen_scsifront]
>>> [ 219.816576] [<ffffffff805a4ee0>] xenbus_dev_remove+0x50/0xa0
>>> [ 219.816580] [<ffffffff805e1a8a>] __device_release_driver+0x7a/0xf0
>>> [ 219.816584] [<ffffffff805e1b1e>] device_release_driver+0x1e/0x30
>>> [ 219.816588] [<ffffffff805e1440>] bus_remove_device+0x100/0x180
>>> [ 219.816593] [<ffffffff805ddef1>] device_del+0x121/0x1b0
>>> [ 219.816596] [<ffffffff805ddf99>] device_unregister+0x19/0x60
>>> [ 219.816601] [<ffffffff805a56be>] xenbus_dev_changed+0x9e/0x1e0
>>> [ 219.816606] [<ffffffff8079d695>] ?
>>> _raw_spin_unlock_irqrestore+0x25/0x50
>>> [ 219.816611] [<ffffffff805a41d0>] ? unregister_xenbus_watch+0x200/0x200
>>> [ 219.816615] [<ffffffff805a7420>] frontend_changed+0x20/0x50
>>> [ 219.816619] [<ffffffff805a426f>] xenwatch_thread+0x9f/0x160
>>> [ 219.816624] [<ffffffff802a50f0>] ? prepare_to_wait_event+0xf0/0xf0
>>> [ 219.816628] [<ffffffff8028485d>] kthread+0xcd/0xf0
>>> [ 219.816633] [<ffffffff80284790>] ? kthread_create_on_node+0x170/0x170
>>> [ 219.816638] [<ffffffff8079dcbc>] ret_from_fork+0x7c/0xb0
>>> [ 219.816642] [<ffffffff80284790>] ? kthread_create_on_node+0x170/0x170
>>> [ 219.816645] Code: 8b af c0 00 00 00 48 c7 c7 c0 08 c7 80 e8 d1 e0 19
>>> 00 49 8b 84 24 c0 00 00 00 8b 90 48 01 00 00 85 d2 74 2f 48 8b 98 50 01
>>> 00 00 <8b> 43 10 85 c0 74 68 83 e8 01 85 c0 89 43 10 74 37 48 c7 c7 c0
>>> [ 219.816732] RIP [<ffffffff805fdcf8>] scsi_put_host_cmd_pool+0x38/0xb0
>>> [ 219.816747] RSP <ffff88003da9fc20>
>>> [ 219.816750] CR2: 0000000000000010
>>> [ 219.816753] ---[ end trace c6915ea21a3d05f7 ]---
>>>
>>> I should mention I've specified .cmd_len in the scsi_host_template. The
>>> only other driver doing this seems to be virtio_scsi.c, so I assume the
>>> same problem could occur with passed-through SCSI devices under KVM...
>>
>> After looking into the code the reason seems to be rather obvious:
>>
>> scsi_find_host_cmd_pool() returns shost->hostt->cmd_pool if .cmd_size is
>> set. But shost->hostt->cmd_pool is never set. The following patch should
>> solve the issue (after testing it I'll send an official patch):
>>
>> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
>> index 88d46fe..da769f9 100644
>> --- a/drivers/scsi/scsi.c
>> +++ b/drivers/scsi/scsi.c
>> @@ -380,6 +380,10 @@ scsi_alloc_host_cmd_pool(struct Scsi_Host *shost)
>> pool->slab_flags |= SLAB_CACHE_DMA;
>> pool->gfp_mask = __GFP_DMA;
>> }
>> +
>> + if (shost->hostt->cmd_size)
>> + shost->hostt->cmd_pool = pool;
>> +
>> return pool;
>> }
>
> I don't think this logic is correct. It's set in
>
> int scsi_setup_command_freelist(struct Scsi_Host *shost)
> {
> const gfp_t gfp_mask = shost->unchecked_isa_dma ? GFP_DMA : GFP_KERNEL;
> struct scsi_cmnd *cmd;
>
> spin_lock_init(&shost->free_list_lock);
> INIT_LIST_HEAD(&shost->free_list);
>
> shost->cmd_pool = scsi_get_host_cmd_pool(shost);
>
> Which should is called from scsi_add_host().
That's only in the Scsi_Host structure, not in the host template, where
scsi_find_host_cmd_pool() is looking for it.
A new pool is created for each new host structure of that driver, thus
there should be a memory leak, too.
> I don't think your analysis above can be correct. If cmd_pool were
> NULL, you'd oops while your driver operates, not just in teardown. So,
> there's something else wrong. Could it be the host wasn't set up
> correctly in the first place and so there's a missing check in the
> teardown routines.
No, my test confirm the patch is correct.
Juergen
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