linux-kernel - RE: [PATCH] scsi: ufs: core: Ensure clk_gating.lock is used only after initialization

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Message-ID:
 <DM6PR04MB657565424F925890D1E1CB3DFCE02@DM6PR04MB6575.namprd04.prod.outlook.com>
Date: Thu, 23 Jan 2025 07:43:24 +0000
From: Avri Altman <Avri.Altman@....com>
To: Bart Van Assche <bvanassche@....org>, "Martin K . Petersen"
	<martin.petersen@...cle.com>
CC: "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Manivannan
 Sadhasivam <manisadhasivam.linux@...il.com>, Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>
Subject: RE: [PATCH] scsi: ufs: core: Ensure clk_gating.lock is used only
 after initialization

> On 1/21/25 10:27 PM, Avri Altman wrote:
> > This commit addresses a lockdep warning triggered by the use of the
> > clk_gating.lock before it is properly initialized. The warning is as
> > follows:
> >
> > [    4.388838] INFO: trying to register non-static key.
> > [    4.395673] The code is fine but needs lockdep annotation, or maybe
> > [    4.402118] you didn't initialize this object before use?
> > [    4.407673] turning off the locking correctness validator.
> > [    4.413334] CPU: 5 UID: 0 PID: 58 Comm: kworker/u32:1 Not tainted 6.12-
> rc1 #185
> > [    4.413343] Hardware name: Qualcomm Technologies, Inc. Robotics RB5
> (DT)
> > [    4.413362] Call trace:
> > [    4.413364]  show_stack+0x18/0x24 (C)
> > [    4.413374]  dump_stack_lvl+0x90/0xd0
> > [    4.413384]  dump_stack+0x18/0x24
> > [    4.413392]  register_lock_class+0x498/0x4a8
> > [    4.413400]  __lock_acquire+0xb4/0x1b90
> > [    4.413406]  lock_acquire+0x114/0x310
> > [    4.413413]  _raw_spin_lock_irqsave+0x60/0x88
> > [    4.413423]  ufshcd_setup_clocks+0x2c0/0x490
> > [    4.413433]  ufshcd_init+0x198/0x10ec
> > [    4.413437]  ufshcd_pltfrm_init+0x600/0x7c0
> > [    4.413444]  ufs_qcom_probe+0x20/0x58
> > [    4.413449]  platform_probe+0x68/0xd8
> > [    4.413459]  really_probe+0xbc/0x268
> > [    4.413466]  __driver_probe_device+0x78/0x12c
> > [    4.413473]  driver_probe_device+0x40/0x11c
> > [    4.413481]  __device_attach_driver+0xb8/0xf8
> > [    4.413489]  bus_for_each_drv+0x84/0xe4
> > [    4.413495]  __device_attach+0xfc/0x18c
> > [    4.413502]  device_initial_probe+0x14/0x20
> > [    4.413510]  bus_probe_device+0xb0/0xb4
> > [    4.413517]  deferred_probe_work_func+0x8c/0xc8
> > [    4.413524]  process_scheduled_works+0x250/0x658
> > [    4.413534]  worker_thread+0x15c/0x2c8
> > [    4.413542]  kthread+0x134/0x200
> > [    4.413550]  ret_from_fork+0x10/0x20
> >
> > To fix this issue, we use the existing `is_initialized` flag in the
> > `clk_gating` structure to ensure that the spinlock is only used after
> > it has been properly initialized. We check this flag before using the
> > spinlock in the `ufshcd_setup_clocks` function.
> >
> > It was incorrect in the first place to call `setup_clocks()` before
> > `ufshcd_init_clk_gating()`, and the introduction of the new lock
> > unmasked this bug.
> >
> > Fixes: 209f4e43b806 ("scsi: ufs: core: Introduce a new clock_gating
> > lock")
> > Reported-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > Signed-off-by: Avri Altman <avri.altman@....com>
> > ---
> >   drivers/ufs/core/ufshcd.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> > index f6c38cf10382..a778fc51ca2a 100644
> > --- a/drivers/ufs/core/ufshcd.c
> > +++ b/drivers/ufs/core/ufshcd.c
> > @@ -9142,7 +9142,7 @@ static int ufshcd_setup_clocks(struct ufs_hba
> *hba, bool on)
> >                       if (!IS_ERR_OR_NULL(clki->clk) && clki->enabled)
> >                               clk_disable_unprepare(clki->clk);
> >               }
> > -     } else if (!ret && on) {
> > +     } else if (!ret && on && hba->clk_gating.is_initialized) {
> >               scoped_guard(spinlock_irqsave, &hba->clk_gating.lock)
> >                       hba->clk_gating.state = CLKS_ON;
> >               trace_ufshcd_clk_gating(dev_name(hba->dev),
> 
> Has it been considered to move the spin_lock_init(&hba->clk_gating.lock)
> call from ufshcd_init_clk_gating() such that it occurs before its first use, e.g.
> just before the ufshcd_hba_init() call in ufshcd_init()?
While your suggestion has merit, it would unfortunately break the fundamental concept of concentrating the initialization logic in one place, which is essential for maintaining a clean and manageable codebase.
Will do that if you think it's better.

Thanks,
Avri

> 
> Thanks,
> 
> Bart.