Re: [PATCH mmc v2] mmc: core: Avoid bitfield RMW for claim/retune flags

[Adrian Hunter <adrian.hunter@intel.com>]

On 19/02/2026 22:29, Penghe Geng wrote:
> Move claimed and retune control flags out of the bitfield word to
> avoid unrelated RMW side effects in asynchronous contexts.
> 
> The host->claimed bit shared a word with retune flags. Writes to claimed
> in __mmc_claim_host() or retune_now in mmc_mq_queue_rq() can overwrite
> other bits when concurrent updates happen in other contexts, triggering
> spurious WARN_ON(!host->claimed). Convert claimed, can_retune,
> retune_now and retune_paused to bool to remove shared-word coupling.
> 
> Fixes: 6c0cedd1ef952 ("mmc: core: Introduce host claiming by context")
> Fixes: 1e8e55b67030c ("mmc: block: Add CQE support")
> Cc: stable@vger.kernel.org
> Suggested-by: Adrian Hunter <adrian.hunter@intel.com>
> Signed-off-by: Penghe Geng <pgeng@nvidia.com>

Acked-by: Adrian Hunter <adrian.hunter@intel.com>

> ---
>  include/linux/mmc/host.h | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index e0e2c265e5d1..ba84f02c2a10 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -486,14 +486,12 @@ struct mmc_host {
>  
>  	struct mmc_ios		ios;		/* current io bus settings */
>  
> +	bool			claimed;	/* host exclusively claimed */
> +
>  	/* group bitfields together to minimize padding */
>  	unsigned int		use_spi_crc:1;
> -	unsigned int		claimed:1;	/* host exclusively claimed */
>  	unsigned int		doing_init_tune:1; /* initial tuning in progress */
> -	unsigned int		can_retune:1;	/* re-tuning can be used */
>  	unsigned int		doing_retune:1;	/* re-tuning in progress */
> -	unsigned int		retune_now:1;	/* do re-tuning at next req */
> -	unsigned int		retune_paused:1; /* re-tuning is temporarily disabled */
>  	unsigned int		retune_crc_disable:1; /* don't trigger retune upon crc */
>  	unsigned int		can_dma_map_merge:1; /* merging can be used */
>  	unsigned int		vqmmc_enabled:1; /* vqmmc regulator is enabled */
> @@ -508,6 +506,9 @@ struct mmc_host {
>  	int			rescan_disable;	/* disable card detection */
>  	int			rescan_entered;	/* used with nonremovable devices */
>  
> +	bool			can_retune;	/* re-tuning can be used */
> +	bool			retune_now;	/* do re-tuning at next req */
> +	bool			retune_paused;	/* re-tuning is temporarily disabled */
>  	int			need_retune;	/* re-tuning is needed */
>  	int			hold_retune;	/* hold off re-tuning */
>  	unsigned int		retune_period;	/* re-tuning period in secs */