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

[Avri Altman <Avri.Altman@wdc.com>]

> Hi Avri,
> 
> Thanks for your patch!
> 
> On Sun, 26 Jan 2025 at 07:48, Avri Altman <avri.altman@wdc.com> 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.
Done. Will remove.

> 
> > 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...
Done. Will rephrase.

Thanks,
Avri
> 
> > 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@linux-m68k.org>
> > Signed-off-by: Avri Altman <avri.altman@wdc.com>
> 
> Seems to work fine on R-Car S4 SK, so
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-
> m68k.org
> 
> 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