linux-kernel - Re: [PATCH] scsi: libsas: Grab the host lock in sas_ata_device_link

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Message-ID: <Y6LVaE5e9iZNAYrF@x1-carbon>
Date:   Wed, 21 Dec 2022 09:44:09 +0000
From:   Niklas Cassel <Niklas.Cassel@....com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>
CC:     Jason Yan <yanaijie@...wei.com>,
        John Garry <john.g.garry@...cle.com>,
        Xingui Yang <yangxingui@...wei.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        "prime.zeng@...ilicon.com" <prime.zeng@...ilicon.com>,
        "kangfenglong@...wei.com" <kangfenglong@...wei.com>
Subject: Re: [PATCH] scsi: libsas: Grab the host lock in
 sas_ata_device_link_abort()

On Wed, Dec 21, 2022 at 05:31:59PM +0900, Damien Le Moal wrote:
> > 
> > What about the interrupt handler such as ahci_error_intr()? I didn't see
> > the callers hold the port lock too. Do they need the port lock?
> 
> It looks like it is missing for ahci_thunderx_irq_handler() but that one
> takes the host lock. Same for xgene_ahci_irq_intr(), again no port lock
> but host lock taken. And again for ahci_single_level_irq_intr() for the
> non MSI case. For modern MSI adapters, the port lock is taken in
> 
> For other cases, ahci_multi_irqs_intr_hard) takes the port lock.
> 
> So it looks like ahci_port_intr() needs to take the lock and some
> cleanups overall (the host lock should not be necessary in the command
> path. But nobody seems to have issues with the "bad" cases... Probably
> because they are not mainstream adapters.
> 
> Definitely some work needed here.

ahci_multi_irqs_intr_hard() takes the ap->lock before calling
ahci_handle_port_interrupt(), which calls ahci_port_intr(),
so I don't think there is any work needed for multi IRQ AHCI.

For ahci_single_level_irq_intr() the host lock is taken before
calling ahci_handle_port_intr(), so I don't see why we need any
extra work for single IRQ AHCI.


Remember, while the default is that:
	ap->lock = &host->lock;
see:
https://github.com/torvalds/linux/blob/v6.1/drivers/ata/libata-core.c#L5305

In case of MULTI MSI, the ap->lock is using its own lock:
https://github.com/torvalds/linux/blob/v6.1/drivers/ata/libahci.c#L2460


So what is it that needs to be fixed for AHCI?

I haven't looked at ahci_thunderx_irq_handler() and xgene_ahci_irq_intr()
so I can't speak for these.


Kind regards,
Niklas