linux-kernel - Re: [PATCH v3] scsi: libsas: Fix set zero-address when device-type != NO

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Message-ID: <dea5cabb-7d9a-44b0-85e4-878c13233f6a@oracle.com>
Date:   Thu, 16 Nov 2023 10:13:19 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Xingui Yang <yangxingui@...wei.com>, yanaijie@...wei.com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        damien.lemoal@...nsource.wdc.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, prime.zeng@...ilicon.com,
        kangfenglong@...wei.com, chenxiang66@...ilicon.com
Subject: Re: [PATCH v3] scsi: libsas: Fix set zero-address when device-type !=
 NO_DEVICE

On 16/11/2023 03:52, Xingui Yang wrote:

I think that patch title can be improved, but I would need to know more 
about the problem before suggesting an improvement.

> Firstly, when ex_phy is added to the parent port, ex_phy->port is not set.

That seems correct, but why mention this now?

> As a result, sas_port_delete_phy() won't be called in
> sas_unregister_devs_sas_addr(), and although ex_phy's sas_address is zero,
> it is not deleted from the parent port's phy_list.

I am not sure why you mention this now either. You seem to be describing 
how the problem occurs without actually mentioning what the problem is.

> 
> Secondly, phy->attached_sas_addr will be set to a zero-address when
> phy->linkrate < SAS_LINK_RATE_1_5_GBPS and device-type != NO_DEVICE during
> device registration, such as stp. It will create a new port and all other
> ex_phys whose addresses are zero will be added to the new port in
> sas_ex_get_linkrate(), and it may trigger BUG() as follows:

I think that it would be better to first mention this crash, i.e. the 
problem, how you recreate it, and then describe how and why it happens, 
and then tell us how you will fix it.

> 
> [562240.051046] sas: phy19 part of wide port with phy16
> [562240.051197] sas: ex 500e004aaaaaaa1f phy19:U:0 attached: 0000000000000000 (no device)
> [562240.051203] sas: done REVALIDATING DOMAIN on port 0, pid:435909, res 0x0
> 
> [562240.062536] sas: ex 500e004aaaaaaa1f phy0 new device attached
> [562240.062616] sas: ex 500e004aaaaaaa1f phy00:U:5 attached: 0000000000000000 (stp)
> [562240.062680]  port-7:7:0: trying to add phy phy-7:7:19 fails: it's already part of another port
> [562240.085064] ------------[ cut here ]------------
> [562240.096612] kernel BUG at drivers/scsi/scsi_transport_sas.c:1083!
> [562240.109611] Internal error: Oops - BUG: 0 [#1] SMP
> [562240.343518] Process kworker/u256:3 (pid: 435909, stack limit = 0x0000000003bcbebf)
> [562240.421714] Workqueue: 0000:b4:02.0_disco_q sas_revalidate_domain [libsas]
> [562240.437173] pstate: 40c00009 (nZcv daif +PAN +UAO)
> [562240.450478] pc : sas_port_add_phy+0x13c/0x168 [scsi_transport_sas]
> [562240.465283] lr : sas_port_add_phy+0x13c/0x168 [scsi_transport_sas]
> [562240.479751] sp : ffff0000300cfa70
> [562240.674822] Call trace:
> [562240.682709]  sas_port_add_phy+0x13c/0x168 [scsi_transport_sas]
> [562240.694013]  sas_ex_get_linkrate.isra.5+0xcc/0x128 [libsas]
> [562240.704957]  sas_ex_discover_end_dev+0xfc/0x538 [libsas]
> [562240.715508]  sas_ex_discover_dev+0x3cc/0x4b8 [libsas]
> [562240.725634]  sas_ex_discover_devices+0x9c/0x1a8 [libsas]
> [562240.735855]  sas_ex_revalidate_domain+0x2f0/0x450 [libsas]
> [562240.746123]  sas_revalidate_domain+0x158/0x160 [libsas]
> [562240.756014]  process_one_work+0x1b4/0x448
> [562240.764548]  worker_thread+0x54/0x468
> [562240.772562]  kthread+0x134/0x138
> [562240.779989]  ret_from_fork+0x10/0x18
> 
> We've done the following to solve this problem:

I'd use "Fix the problem as follows:""

> Firstly, set ex_phy->port when ex_phy is added to the parent port. And set
> ex_dev->parent_port to NULL when the number of PHYs of the parent port
> becomes 0.

Thanks,
John