linux-kernel - RE: [PATCH] bus: fsl-mc: allocate resources when there is no scan in progress

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Message-ID: <VI1PR0402MB3871B6D74FF14A355C6B7AC1E0B30@VI1PR0402MB3871.eurprd04.prod.outlook.com>
Date:   Mon, 25 May 2020 16:13:23 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Laurentiu Tudor <laurentiu.tudor@....com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] bus: fsl-mc: allocate resources when there is no scan in
 progress

> Subject: [PATCH] bus: fsl-mc: allocate resources when there is no scan in
> progress
> 
> Allocate resources from the fsl-mc bus only when a scan of the bus is not
> happening. This is useful when functional devices on the bus, such as DPNI,
> DPSW etc, request some kind of allocatable object but the scan of the bus is still
> in progress, thus those resources are not yet available. Catch this early and
> notify the upper layer driver of the condition.
> 
> Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>
> ---

Please don't apply this.
I just discovered a corner case in which this approach does not work.

Sorry for the bother,
Ioana

>  drivers/bus/fsl-mc/fsl-mc-allocator.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/fsl-mc/fsl-mc-allocator.c b/drivers/bus/fsl-mc/fsl-mc-
> allocator.c
> index cc7bb900f524..794ddc9589dc 100644
> --- a/drivers/bus/fsl-mc/fsl-mc-allocator.c
> +++ b/drivers/bus/fsl-mc/fsl-mc-allocator.c
> @@ -184,6 +184,9 @@ int __must_check fsl_mc_resource_allocate(struct
> fsl_mc_bus *mc_bus,
>  	BUILD_BUG_ON(ARRAY_SIZE(fsl_mc_pool_type_strings) !=
>  		     FSL_MC_NUM_POOL_TYPES);
> 
> +	if (!mutex_trylock(&mc_bus->scan_mutex))
> +		return -ENXIO;
> +
>  	*new_resource = NULL;
>  	if (pool_type < 0 || pool_type >= FSL_MC_NUM_POOL_TYPES)
>  		goto out;
> @@ -197,7 +200,7 @@ int __must_check fsl_mc_resource_allocate(struct
> fsl_mc_bus *mc_bus,
>  					    struct fsl_mc_resource, node);
> 
>  	if (!resource) {
> -		error = -ENXIO;
> +		error = -ENOMEM;
>  		dev_err(&mc_bus_dev->dev,
>  			"No more resources of type %s left\n",
>  			fsl_mc_pool_type_strings[pool_type]);
> @@ -220,6 +223,7 @@ int __must_check fsl_mc_resource_allocate(struct
> fsl_mc_bus *mc_bus,
>  	mutex_unlock(&res_pool->mutex);
>  	*new_resource = resource;
>  out:
> +	mutex_unlock(&mc_bus->scan_mutex);
>  	return error;
>  }
>  EXPORT_SYMBOL_GPL(fsl_mc_resource_allocate);
> --
> 2.17.1