Re: [PATCH v3 2/2] scsi: ufs: Fix toggling of clk_gating.state when clock gating is not allowed

[Geert Uytterhoeven]

Hi Avri,

Thanks for your patch!

On Sun, 26 Jan 2025 at 07:48, Avri Altman <avri.altman@xxxxxxx> wrote:
> This commit addresses an issue where `clk_gating.state` is being toggled
> in `ufshcd_setup_clocks` even if clock gating is not allowed. This can
> lead to a crash with the following error:
>
>     BUG: spinlock bad magic on CPU#6, swapper/0/1
>      lock: 0xffffff84443014e8, .magic: 00000000, .owner: <none>/-1,
>     .owner_cpu: 0
>     CPU: 6 UID: 0 PID: 1 Comm: swapper/0 Not tainted
>     6.13.0-rcar3-initrd-08318-g75abbef32a94 #896
>     Hardware name: R-Car S4 Starter Kit board (DT)
>     Call trace:
>      show_stack+0x18/0x24 (C)
>      dump_stack_lvl+0x60/0x80
>      dump_stack+0x18/0x24
>      spin_bug+0x7c/0xa0
>      do_raw_spin_lock+0x34/0xb4
>      _raw_spin_lock_irqsave+0x1c/0x30
>      class_spinlock_irqsave_constructor+0x18/0x30
>      ufshcd_setup_clocks+0x98/0x23c
>      ufshcd_init+0x288/0xd38
>      ufshcd_pltfrm_init+0x618/0x738
>      ufs_renesas_probe+0x18/0x24
>      platform_probe+0x68/0xb8
>      really_probe+0x138/0x268
>      __driver_probe_device+0xf4/0x10c
>      driver_probe_device+0x3c/0xf8
>      __driver_attach+0xf0/0x100
>      bus_for_each_dev+0x84/0xdc
>      driver_attach+0x24/0x30
>      bus_add_driver+0xe8/0x1dc
>      driver_register+0xbc/0xf8
>      __platform_driver_register+0x24/0x30
>      ufs_renesas_platform_init+0x1c/0x28
>      do_one_initcall+0x84/0x1f4
>      kernel_init_freeable+0x238/0x23c
>      kernel_init+0x20/0x120
>      ret_from_fork+0x10/0x20

Note that after "[PATCH v3 1/2] scsi: ufs: core: Ensure clk_gating.lock
is used only after initialization", I no longer see the above BUG(), so
I don't think it's a good idea to include this log.

> The root cause of the issue is that `clk_gating.state` is being toggled
> even if clock gating is not allowed. This can lead to the spinlock being
> used before it is properly initialized.

Which doesn't mean the underlying issue no longer exists...

> The fix is to add a check for `hba->clk_gating.is_initialized` before
> toggling `clk_gating.state` in `ufshcd_setup_clocks`. Since
> `clk_gating.lock` is now initialized unconditionally, this is for
> documentation purposes, to ensure clarity in the code. The primary fix
> remains to prevent toggling the `clk_gating.state` if clock gating is
> not allowed.
>
> Fixes: 1ab27c9cf8b6 ("ufs: Add support for clock gating")
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Signed-off-by: Avri Altman <avri.altman@xxxxxxx>

Seems to work fine on R-Car S4 SK, so
Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds