Messages in this thread | | | Subject | Re: [PATCH] clk: vc5: Fix div-by-0 when rounding a rate of zero | From | Marek Vasut <> | Date | Thu, 31 May 2018 21:37:08 +0200 |
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On 05/31/2018 08:52 PM, Steve Longerbeam wrote: > > > On 05/31/2018 11:35 AM, Marek Vasut wrote: >> On 05/31/2018 08:32 PM, Steve Longerbeam wrote: >>> Hi Marek, >>> >>> >>> On 05/31/2018 11:25 AM, Marek Vasut wrote: >>>> On 05/31/2018 08:23 PM, Steve Longerbeam wrote: >>>>> Just return zero for a rounded rate if requested rate is zero. >>>>> >>>>> This was caught by CONFIG_UBSAN: >>>>> >>>>> [ 192.266748] UBSAN: Undefined behaviour in >>>>> drivers/clk/clk-versaclock5.c:513:17 >>>>> [ 192.274050] division by zero >>>>> [ 192.276976] CPU: 0 PID: 2579 Comm: vsp-unit-test-0 Tainted: G >>>>> B WC 4.14.17-02752-g13fb96f #1 >>>>> [ 192.286378] Hardware name: Renesas Salvator-X board based on >>>>> r8a7795 ES2.0+ (DT) >>>>> [ 192.293852] Call trace: >>>>> [ 192.296343] [<ffff2000080900dc>] dump_backtrace+0x0/0x390 >>>>> [ 192.301807] [<ffff200008090480>] show_stack+0x14/0x1c >>>>> [ 192.306920] [<ffff200008f66574>] dump_stack+0x134/0x1a8 >>>>> [ 192.312213] [<ffff2000087aaa30>] ubsan_epilogue+0x14/0x60 >>>>> [ 192.317677] [<ffff2000087ab4d0>] >>>>> __ubsan_handle_divrem_overflow+0x11c/0x170 >>>>> [ 192.324720] [<ffff200008852120>] vc5_fod_round_rate+0x68/0x148 >>>>> [ 192.330620] [<ffff20000884567c>] clk_calc_new_rates+0x238/0x3fc >>>>> [ 192.336607] [<ffff2000088456e0>] clk_calc_new_rates+0x29c/0x3fc >>>>> [ 192.342595] [<ffff2000088483ac>] >>>>> clk_core_set_rate_nolock+0x48/0x11c >>>>> [ 192.349019] [<ffff2000088484b4>] clk_set_rate+0x34/0x4c >>>>> [ 192.354307] [<ffff20000895e304>] rcar_du_pm_suspend+0x274/0x2f4 >>>>> [ 192.360297] [<ffff20000898feac>] platform_pm_suspend+0x78/0xb8 >>>>> [ 192.366198] [<ffff2000089a5604>] dpm_run_callback+0x584/0xa18 >>>>> [ 192.372010] [<ffff2000089a69e0>] __device_suspend+0x1a8/0x534 >>>>> [ 192.377822] [<ffff2000089adc48>] dpm_suspend+0x130/0xea0 >>>>> [ 192.383197] [<ffff2000089b0344>] dpm_suspend_start+0x130/0x138 >>>>> [ 192.389099] [<ffff20000817f584>] >>>>> suspend_devices_and_enter+0xf0/0x1778 >>>>> [ 192.395700] [<ffff200008183014>] pm_suspend+0x2408/0x245c >>>>> [ 192.401162] [<ffff20000817c0a4>] state_store+0xf0/0x130 >>>>> [ 192.406451] [<ffff200008f6f19c>] kobj_attr_store+0x5c/0x6c >>>>> [ 192.412002] [<ffff2000084f4c94>] sysfs_kf_write+0xe8/0xfc >>>>> [ 192.417466] [<ffff2000084f30b0>] kernfs_fop_write+0x22c/0x2e4 >>>>> [ 192.423281] [<ffff2000083e46d4>] __vfs_write+0x104/0x34c >>>>> [ 192.428656] [<ffff2000083e4cc4>] vfs_write+0x134/0x2d8 >>>>> [ 192.433857] [<ffff2000083e5150>] SyS_write+0xbc/0x12c >>>>> [ 192.438967] Exception stack(0xffff8006cd1cfec0 to >>>>> 0xffff8006cd1d0000) >>>>> [ 192.445480] fec0: 0000000000000001 000000001e303f00 >>>>> 0000000000000004 0000ffff959a5000 >>>>> [ 192.453397] fee0: 0000000000000000 0000000155510004 >>>>> 0000000000000003 000000000000006d >>>>> [ 192.461314] ff00: 0000000000000040 0000000000000000 >>>>> 0000ffffcc304800 0000000000000020 >>>>> [ 192.469230] ff20: 0000000000000000 0000000000000000 >>>>> 0000000000000001 0000000000000008 >>>>> [ 192.477148] ff40: 00000000004eb3b8 0000ffff958bb840 >>>>> 000000000000003d 0000000000000001 >>>>> [ 192.485065] ff60: 000000001e303f00 0000ffff959a1508 >>>>> 0000000000000004 000000001e303f00 >>>>> [ 192.492982] ff80: 0000000000000004 00000000004d4c68 >>>>> 0000000000000001 0000000000000000 >>>>> [ 192.500899] ffa0: 000000001e30d5c0 0000ffffcc304820 >>>>> 0000ffff958bec64 0000ffffcc304820 >>>>> [ 192.508816] ffc0: 0000ffff95912898 0000000020000000 >>>>> 0000000000000001 0000000000000040 >>>>> [ 192.516733] ffe0: 0000000000000000 0000000000000000 >>>>> 0000000000000000 0000000000000000 >>>>> [ 192.524650] [<ffff200008083ef0>] el0_svc_naked+0x24/0x28 >>>>> >>>>> Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com> >>>>> --- >>>>> drivers/clk/clk-versaclock5.c | 4 ++++ >>>>> 1 file changed, 4 insertions(+) >>>>> >>>>> diff --git a/drivers/clk/clk-versaclock5.c >>>>> b/drivers/clk/clk-versaclock5.c >>>>> index decffb3..113523d 100644 >>>>> --- a/drivers/clk/clk-versaclock5.c >>>>> +++ b/drivers/clk/clk-versaclock5.c >>>>> @@ -509,6 +509,10 @@ static long vc5_fod_round_rate(struct clk_hw >>>>> *hw, unsigned long rate, >>>>> u32 div_int; >>>>> u64 div_frc; >>>>> + /* prevent div-by-0 */ >>>>> + if (rate == 0) >>>>> + return 0; >>>>> + >>>>> /* Determine integer part, which is 12 bit wide */ >>>>> div_int = f_in / rate; >>>>> /* >>>>> >>>> Can this actually happen ? >>> We caught this using the Renesas 3.6.0 BSP release, when performing >>> a suspend of rcar-du driver. The rcar_du_pm_suspend() in 3.6.0 BSP is >>> modified >>> from mainline version, including calling clk_set_rate() on the crtc >>> clocks with a >>> rate of zero. So this is not actually reproducible (yet) in mainline. >> So it sets clock to 0 ? > > Yep, see > > https://kernel.googlesource.com/pub/scm/linux/kernel/git/horms/renesas-bsp/+/rcar-3.6.0/drivers/gpu/drm/rcar-du/rcar_du_drv.c#359 > > >> Anyway, this looks sane, although maybe the >> whole driver could use a once-over to see if there could be more of this. > > Actually I do see more potential divide-by-zeros due to a passed rate > of zero, including vc5_pfd_round_rate() and vc5_pfd_set_rate(). > > I can resubmit this patch fixing all cases in clk-versaclock5.c if you > like (and probably remove the misleading backtrace in the commit > message since it is a Renesas 3.6.0 kernel backtrace not a mainline > backtrace). > > Or perhaps just treat this as a heads-up, I'll leave it up to you.
It'd be nice if you resubmitted it fixing all the cases.
>> Or should the clock framework even let us set clock to 0 Hz ? > > That is a good question, it might make sense for the core clock framework > to not allow passing a rate of 0 on to the clock ops, and instead treat > it generically.
Jupp
-- Best regards, Marek Vasut
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