Re: [PATCH v2] i2c: i801: fix hardware state machine corruption in error path

[Andi Shyti <andi.shyti@kernel.org>]

Hi Jean,

could you please take a look here?

Thanks,
Andi

On Tue, May 12, 2026 at 05:35:34PM +0800, w15303746062@163.com wrote:
> From: Mingyu Wang <25181214217@stu.xidian.edu.cn>
> 
> A severe livelock and subsequent Hung Task panic were observed in the
> i2c-i801 driver during concurrent Fuzzing. The crash is caused by an
> unconditional hardware register cleanup in the error handling path of
> i801_access().
> 
> When i801_check_pre() fails (e.g., returning -EBUSY because the SMBus
> controller is actively used by BIOS/ACPI), the kernel does not actually
> acquire the hardware ownership. However, the code jumps to the 'out'
> label and executes:
> 
>     iowrite8(SMBHSTSTS_INUSE_STS | STATUS_FLAGS, SMBHSTSTS(priv));
> 
> This forcefully clears the INUSE_STS lock and resets the hardware status
> flags without owning the controller. Doing so interrupts ongoing BIOS/ACPI
> transactions and totally corrupts the SMBus hardware state machine.
> 
> Consequently, all subsequent i801_access() calls fail at the pre-check
> stage, triggering an endless stream of "SMBus is busy, can't use it!"
> error logs. Over a slow serial console, this printk flood monopolizes
> the CPU (Console Livelock), starving other processes trying to acquire
> the mmap_lock down_read semaphore, ultimately triggering the hung task
> watchdog.
> 
> Fix this by moving the 'out' label below the hardware register cleanup.
> If i801_check_pre() fails, we safely bypass the iowrite8() and only
> release the software locks (pm_runtime and mutex), strictly adhering to
> the rule of not releasing resources that were never acquired.
> 
> Fixes: 1f760b87e54c ("i2c: i801: Call i801_check_pre() from i801_access()")
> Cc: stable@vger.kernel.org # v6.3+
> 
> Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn>
> ---
> Changes in v2:
>  - Reused and moved the existing 'out' label instead of adding a new one,
>    fixing a build warning regarding an unused label.
>  - Dropped the inaccurate mention of "another thread" in the commit message,
>    as i801_access() is serialized by a mutex.
>  - Added Fixes and Cc stable tags as suggested.
> 
>  drivers/i2c/busses/i2c-i801.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
> index 32a3cef02c7b..b29c99ed3883 100644
> --- a/drivers/i2c/busses/i2c-i801.c
> +++ b/drivers/i2c/busses/i2c-i801.c
> @@ -931,13 +931,13 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  	 */
>  	if (hwpec)
>  		iowrite8(ioread8(SMBAUXCTL(priv)) & ~SMBAUXCTL_CRC, SMBAUXCTL(priv));
> -out:
>  	/*
>  	 * Unlock the SMBus device for use by BIOS/ACPI,
>  	 * and clear status flags if not done already.
>  	 */
>  	iowrite8(SMBHSTSTS_INUSE_STS | STATUS_FLAGS, SMBHSTSTS(priv));
>  
> +out:
>  	pm_runtime_put_autosuspend(&priv->pci_dev->dev);
>  	mutex_unlock(&priv->acpi_lock);
>  	return ret;
> -- 
> 2.34.1
>