linux-kernel - Re: [PATCH v2] scsi: pm8001: Fix data race in sysfs SAS address read

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Message-ID: <CAMGffEk3cgah3-xTaokDeiM0RGwKQn1OO43dWLJAwoaVDfHWdQ@mail.gmail.com>
Date: Fri, 16 Jan 2026 06:46:28 +0100
From: Jinpu Wang <jinpu.wang@...os.com>
To: Chengfeng Ye <dg573847474@...il.com>
Cc: "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>, 
	"Martin K . Petersen" <martin.petersen@...cle.com>, Bart Van Assche <bvanassche@....org>, 
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chengfeng Ye <cyeaa@...nect.ust.hk>
Subject: Re: [PATCH v2] scsi: pm8001: Fix data race in sysfs SAS address read

On Thu, Jan 15, 2026 at 6:55 PM Chengfeng Ye <dg573847474@...il.com> wrote:
>
> From: Chengfeng Ye <cyeaa@...nect.ust.hk>
>
> Fix a data race where pm8001_ctl_host_sas_address_show() reads
> pm8001_ha->sas_addr without synchronization while it can be written
> from interrupt context in pm8001_mpi_get_nvmd_resp().
>
> The write path is already protected by pm8001_ha->lock (held by
> process_oq() when calling pm8001_mpi_get_nvmd_resp()),
> but the sysfs read path accesses the 8-byte SAS address without
> any synchronization, allowing torn reads.
>
> Thread interleaving scenario:
>
>            Thread A (sysfs read)     |    Thread B (interrupt context)
> -------------------------------------+------------------------------------
> pm8001_ctl_host_sas_address_show()  |
> |- read sas_addr[0..3]               |
>                                      | process_oq()
>                                      | |- spin_lock_irqsave(&lock)
>                                      | |- process_one_iomb()
>                                      | |  |- pm8001_mpi_get_nvmd_resp()
>                                      | |     |- memcpy(sas_addr, new, 8)
>                                      | |        /* writes all 8 bytes */
>                                      | |- spin_unlock_irqrestore(&lock)
> |- read sas_addr[4..7]               |
>    /* gets mix of old and new */    |
>
> Fix by protecting the sysfs read with the same pm8001_ha->lock
> using guard(spinlock_irqsave) for automatic lock cleanup.
>
> Signed-off-by: Chengfeng Ye <cyeaa@...nect.ust.hk>
As James commented, sas address is uniq, not something changing all the time.
Do you see any real issue?
> ---
> V1 -> V2: Use guard instead of lock/unlock pair
>
>  drivers/scsi/pm8001/pm8001_ctl.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/scsi/pm8001/pm8001_ctl.c b/drivers/scsi/pm8001/pm8001_ctl.c
> index cbfda8c04e95..200ee6bbd413 100644
> --- a/drivers/scsi/pm8001/pm8001_ctl.c
> +++ b/drivers/scsi/pm8001/pm8001_ctl.c
> @@ -311,6 +311,8 @@ static ssize_t pm8001_ctl_host_sas_address_show(struct device *cdev,
>         struct Scsi_Host *shost = class_to_shost(cdev);
>         struct sas_ha_struct *sha = SHOST_TO_SAS_HA(shost);
>         struct pm8001_hba_info *pm8001_ha = sha->lldd_ha;
> +
> +       guard(spinlock_irqsave)(&pm8001_ha->lock);
>         return sysfs_emit(buf, "0x%016llx\n",
>                         be64_to_cpu(*(__be64 *)pm8001_ha->sas_addr));
>  }
> --
> 2.25.1
>