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

Seung-Woo Kim
2016-06-20T03:30:28Z

Hello Jaehoon,

> -----Original Message-----
> From: Jaehoon Chung [mailto:jh80.chung@samsung.com]
> Sent: Monday, June 20, 2016 11:34 AM
> To: Seung-Woo Kim; ulf.hansson@linaro.org; linux-mmc@vger.kernel.org; linux-kernel@vger.kernel.org
> 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@samsung.com>
> > ---
> > 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
> >