RE: [PATCH v2] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()

[Seung-Woo Kim]

Hello Jaehoon,

> -----Original Message-----
> From: Jaehoon Chung [mailto:jh80.chung@xxxxxxxxxxx]
> Sent: Monday, June 20, 2016 11:34 AM
> To: Seung-Woo Kim; ulf.hansson@xxxxxxxxxx; linux-mmc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2] mmc: dw_mmc: remove UBSAN warning in dw_mci_setup_bus()
> 
> Hi SeungWoo,
> 
> On 06/17/2016 02:16 PM, Seung-Woo Kim wrote:
> > This patch removes following UBSAN warnings in dw_mci_setup_bus().
> >
> >   UBSAN: Undefined behaviour in drivers/mmc/host/dw_mmc.c:1102:14
> >   shift exponent 250 is too large for 32-bit type 'unsigned int'
> >   Call trace:
> >   [<ffffff90080908a8>] dump_backtrace+0x0/0x380
> >   [<ffffff9008090c3c>] show_stack+0x14/0x20
> >   [<ffffff90087457b8>] dump_stack+0xe0/0x120
> >   [<ffffff90087b1360>] ubsan_epilogue+0x18/0x68
> >   [<ffffff90087b1a94>] __ubsan_handle_shift_out_of_bounds+0x18c/0x1bc
> >   [<ffffff9008d89cb8>] dw_mci_setup_bus+0x3a0/0x438
> >   [...]
> >
> >   UBSAN: Undefined behaviour in drivers/mmc/host/dw_mmc.c:1132:27
> >   shift exponent 250 is too large for 32-bit type 'unsigned int'
> >   Call trace:
> >   [<ffffff90080908a8>] dump_backtrace+0x0/0x380
> >   [<ffffff9008090c3c>] show_stack+0x14/0x20
> >   [<ffffff90087457b8>] dump_stack+0xe0/0x120
> >   [<ffffff90087b1360>] ubsan_epilogue+0x18/0x68
> >   [<ffffff90087b1a94>] __ubsan_handle_shift_out_of_bounds+0x18c/0x1bc
> >   [<ffffff9008d89c9c>] dw_mci_setup_bus+0x384/0x438
> >   [...]
> >
> > The warnings are caused because of shift with more than 31 on 32
> > bit variable, so this patch fixes to keep both clock and divider
> > instead of shift.
> >
> > Signed-off-by: Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx>
> > ---
> >  drivers/mmc/host/dw_mmc.c |    8 +++++---
> >  drivers/mmc/host/dw_mmc.h |    8 +++++---
> >  2 files changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> > index 2cc6123..d05c8cc 100644
> > --- a/drivers/mmc/host/dw_mmc.c
> > +++ b/drivers/mmc/host/dw_mmc.c
> > @@ -1099,7 +1099,8 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
> >
> >  		div = (host->bus_hz != clock) ? DIV_ROUND_UP(div, 2) : 0;
> >
> > -		if ((clock << div) != slot->__clk_old || force_clkinit)
> > +		if (clock != slot->__clk_old || div != slot->__div_old ||
> > +		    force_clkinit)
> 
> I have realized why we put this condition..after checking your below codes.
> This was patch to avoid the spamming for CONFIG_MMC_CLKGATE..
> but CONFIG_MMC_CLKAGET didn't use anymore.. I think we can remove this condition.
> 
> How about?

There is no CONFIG_MMC_CLKAGET, but message is still printed. So without
the condition check, there will be too much log. If you will just remove
below print, then I agree about removing the condition and __clk_old, instead
of my patch.

Thanks,
- Seung-Woo Kim

> 
> Best Regards,
> Jaehoon Chung
> 
> >  			dev_info(&slot->mmc->class_dev,
> >  				 "Bus speed (slot %d) = %dHz (slot req %dHz, actual %dHZ div = %d)\n",
> >  				 slot->id, host->bus_hz, clock,
> > @@ -1128,8 +1129,9 @@ static void dw_mci_setup_bus(struct dw_mci_slot *slot, bool force_clkinit)
> >  		/* inform CIU */
> >  		mci_send_cmd(slot, sdmmc_cmd_bits, 0);
> >
> > -		/* keep the clock with reflecting clock dividor */
> > -		slot->__clk_old = clock << div;
> > +		/* keep the clock and clock divider */
> > +		slot->__clk_old = clock;
> > +		slot->__div_old = div;
> >  	}
> >
> >  	host->current_speed = clock;
> > diff --git a/drivers/mmc/host/dw_mmc.h b/drivers/mmc/host/dw_mmc.h
> > index 1e8d838..fdfc3f5 100644
> > --- a/drivers/mmc/host/dw_mmc.h
> > +++ b/drivers/mmc/host/dw_mmc.h
> > @@ -245,9 +245,10 @@ extern int dw_mci_resume(struct dw_mci *host);
> >   * @queue_node: List node for placing this node in the @queue list of
> >   *	&struct dw_mci.
> >   * @clock: Clock rate configured by set_ios(). Protected by host->lock.
> > - * @__clk_old: The last updated clock with reflecting clock divider.
> > - *	Keeping track of this helps us to avoid spamming the console
> > - *	with CONFIG_MMC_CLKGATE.
> > + * @__clk_old: The last updated clock.
> > + * @__div_old: The last updated clock divider.
> > + *	Keeping track of clock and clock divider helps us to avoid spamming
> > + *	the console with CONFIG_MMC_CLKGATE.
> >   * @flags: Random state bits associated with the slot.
> >   * @id: Number of this slot.
> >   * @sdio_id: Number of this slot in the SDIO interrupt registers.
> > @@ -263,6 +264,7 @@ struct dw_mci_slot {
> >
> >  	unsigned int		clock;
> >  	unsigned int		__clk_old;
> > +	unsigned int		__div_old;
> >
> >  	unsigned long		flags;
> >  #define DW_MMC_CARD_PRESENT	0
> >