linux-kernel - Re: [PATCH] scsi: ata: Fix a race condition between scsi error handler and ahci interrupt

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Message-ID: <ZOSONbLwc6RtQnS0@x1-carbon>
Date:   Tue, 22 Aug 2023 10:30:14 +0000
From:   Niklas Cassel <Niklas.Cassel@....com>
To:     Li Nan <linan666@...weicloud.com>
CC:     "dlemoal@...nel.org" <dlemoal@...nel.org>,
        "linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yukuai3@...wei.com" <yukuai3@...wei.com>,
        "yi.zhang@...wei.com" <yi.zhang@...wei.com>,
        "houtao1@...wei.com" <houtao1@...wei.com>,
        "yangerkun@...wei.com" <yangerkun@...wei.com>
Subject: Re: [PATCH] scsi: ata: Fix a race condition between scsi error
 handler and ahci interrupt

On Tue, Aug 22, 2023 at 05:20:33PM +0800, Li Nan wrote:
> Thanks for your reply, Niklas.
> 
> 在 2023/8/21 21:51, Niklas Cassel 写道:
> > On Thu, Aug 10, 2023 at 09:48:48AM +0800, linan666@...weicloud.com wrote:
> 
> [snip]
> 
> > 
> > Hello Li Nan,
> > 
> > I do not understand why the code in:
> > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L722-L731
> > 
> > does not kick in, and repeats EH.
> > 
> > 
> > EH_PENDING is cleared before ->error_handler() is called:
> > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L697
> > 
> > So ahci_error_intr() from the second error interrupt, which is called after
> > thawing the port, should have called ata_std_sched_eh(), which calls
> > ata_eh_set_pending(), which should have set EH_PENDING:
> > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L884
> > 
> > 
> > 
> > My only guess is that after thawing the port:
> > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L2807
> > 
> > The second error irq comes, and sets EH_PENDING,
> > but then this silly code might clear it:
> > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L2825-L2837
> > 
> 
> Yeah, I think so.
> 
> > I think the best way would be if we could improve this "spurious error
> > condition check"... because if this is indeed the code that clears EH_PENDING
> > for you, then this code basically makes the "goto repeat" code in
> > ata_scsi_port_error_handler() useless...
> > 
> > 
> > An alternative to improving the "spurious error condition check" might be for
> > you to try something like:
> > 
> 
> We have used this solution before, but it will case WARN_ON in
> ata_eh_finish() as below:
> 
>   WARNING: CPU: 1 PID: 118 at ../drivers/ata/libata-eh.c:4016
> ata_eh_finish+0x15a/0x170

Ok.

How about if you simply move the WARN_ON to ata_scsi_port_error_handler()
as well:

diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
index 35e03679b0bf..5be2fc651131 100644
--- a/drivers/ata/libata-eh.c
+++ b/drivers/ata/libata-eh.c
@@ -741,6 +741,12 @@ void ata_scsi_port_error_handler(struct Scsi_Host *host, struct ata_port *ap)
                 */
                ap->ops->end_eh(ap);
 
+               if (!ap->scsi_host->host_eh_scheduled) {
+                       /* make sure nr_active_links is zero after EH */
+                       WARN_ON(ap->nr_active_links);
+                       ap->nr_active_links = 0;
+               }
+
                spin_unlock_irqrestore(ap->lock, flags);
                ata_eh_release(ap);
        } else {
@@ -962,7 +968,7 @@ void ata_std_end_eh(struct ata_port *ap)
 {
        struct Scsi_Host *host = ap->scsi_host;
 
-       host->host_eh_scheduled = 0;
+       host->host_eh_scheduled--;
 }
 EXPORT_SYMBOL(ata_std_end_eh);
 
@@ -3948,10 +3954,6 @@ void ata_eh_finish(struct ata_port *ap)
                        }
                }
        }
-
-       /* make sure nr_active_links is zero after EH */
-       WARN_ON(ap->nr_active_links);
-       ap->nr_active_links = 0;
 }
 
 /**



Kind regards,
Niklas