linux-kernel - Re: [PATCH] scsi/atari_scsi: Fix race condition between .queuecommand and EH

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Date:   Fri, 20 Nov 2020 20:33:43 +1300
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Finn Thain <fthain@...egraphics.com.au>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi/atari_scsi: Fix race condition between .queuecommand
 and EH

Hi Finn,

thanks for your patch!

Tested on Atari Falcon (with falconide, and pata_falcon modules).

Reviewed-by: Michael Schmitz <schmitzmic@...il.com>
Tested-by: Michael Schmitz <schmitzmic@...il.com>

Am 20.11.2020 um 17:39 schrieb Finn Thain:
> It is possible that bus_reset_cleanup() or .eh_abort_handler could
> be invoked during NCR5380_queuecommand(). If that takes place before
> the new command is enqueued and after the ST-DMA "lock" has been
> acquired, the ST-DMA "lock" will be released again. This will result
> in a lost DMA interrupt and a command timeout. Fix this by excluding
> EH and interrupt handlers while the new command is enqueued.
>
> Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
> ---
> Michael, would you please send your Acked-by or Reviewed-and-tested-by?
> These two patches taken together should be equivalent to the one you tested
> recently. I've split it into two as that seemed to make more sense.
> ---
>  drivers/scsi/NCR5380.c    |  9 ++++++---
>  drivers/scsi/atari_scsi.c | 10 +++-------
>  2 files changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/scsi/NCR5380.c b/drivers/scsi/NCR5380.c
> index d654a6cc4162..ea4b5749e7da 100644
> --- a/drivers/scsi/NCR5380.c
> +++ b/drivers/scsi/NCR5380.c
> @@ -580,11 +580,14 @@ static int NCR5380_queue_command(struct Scsi_Host *instance,
>
>  	cmd->result = 0;
>
> -	if (!NCR5380_acquire_dma_irq(instance))
> -		return SCSI_MLQUEUE_HOST_BUSY;
> -
>  	spin_lock_irqsave(&hostdata->lock, flags);
>
> +	if (!NCR5380_acquire_dma_irq(instance)) {
> +		spin_unlock_irqrestore(&hostdata->lock, flags);
> +
> +		return SCSI_MLQUEUE_HOST_BUSY;
> +	}
> +
>  	/*
>  	 * Insert the cmd into the issue queue. Note that REQUEST SENSE
>  	 * commands are added to the head of the queue since any command will
> diff --git a/drivers/scsi/atari_scsi.c b/drivers/scsi/atari_scsi.c
> index a82b63a66635..95d7a3586083 100644
> --- a/drivers/scsi/atari_scsi.c
> +++ b/drivers/scsi/atari_scsi.c
> @@ -376,15 +376,11 @@ static int falcon_get_lock(struct Scsi_Host *instance)
>  	if (IS_A_TT())
>  		return 1;
>
> -	if (stdma_is_locked_by(scsi_falcon_intr) &&
> -	    instance->hostt->can_queue > 1)
> +	if (stdma_is_locked_by(scsi_falcon_intr))
>  		return 1;
>
> -	if (in_interrupt())
> -		return stdma_try_lock(scsi_falcon_intr, instance);
> -
> -	stdma_lock(scsi_falcon_intr, instance);
> -	return 1;
> +	/* stdma_lock() may sleep which means it can't be used here */
> +	return stdma_try_lock(scsi_falcon_intr, instance);
>  }
>
>  #ifndef MODULE
>