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Subject: Re: [PATCH] i2c: iproc: fix race between client unreg and isr
To:     Dhananjay Phadke <dphadke@linux.microsoft.com>,
        Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Wolfram Sang <wsa@kernel.org>
Cc:     Ray Jui <rjui@broadcom.com>, bcm-kernel-feedback-list@broadcom.com
References: <1595115599-100054-1-git-send-email-dphadke@linux.microsoft.com>
From:   Ray Jui <ray.jui@broadcom.com>
Message-ID: <116ac90c-8b49-ca89-90a4-9a28f43a7c50@broadcom.com>
Date:   Mon, 20 Jul 2020 10:49:06 -0700
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On 7/18/2020 4:39 PM, Dhananjay Phadke wrote:
> When i2c client unregisters, synchronize irq before setting
> iproc_i2c->slave to NULL.
> 
> Unable to handle kernel NULL pointer dereference at virtual address 0000000000000318
> 
> [  371.020421] pc : bcm_iproc_i2c_isr+0x530/0x11f0
> [  371.025098] lr : __handle_irq_event_percpu+0x6c/0x170
> [  371.030309] sp : ffff800010003e40
> [  371.033727] x29: ffff800010003e40 x28: 0000000000000060
> [  371.039206] x27: ffff800010ca9de0 x26: ffff800010f895df
> [  371.044686] x25: ffff800010f18888 x24: ffff0008f7ff3600
> [  371.050165] x23: 0000000000000003 x22: 0000000001600000
> [  371.055645] x21: ffff800010f18888 x20: 0000000001600000
> [  371.061124] x19: ffff0008f726f080 x18: 0000000000000000
> [  371.066603] x17: 0000000000000000 x16: 0000000000000000
> [  371.072082] x15: 0000000000000000 x14: 0000000000000000
> [  371.077561] x13: 0000000000000000 x12: 0000000000000001
> [  371.083040] x11: 0000000000000000 x10: 0000000000000040
> [  371.088519] x9 : ffff800010f317c8 x8 : ffff800010f317c0
> [  371.093999] x7 : ffff0008f805b3b0 x6 : 0000000000000000
> [  371.099478] x5 : ffff0008f7ff36a4 x4 : ffff8008ee43d000
> [  371.104957] x3 : 0000000000000000 x2 : ffff8000107d64c0
> [  371.110436] x1 : 00000000c00000af x0 : 0000000000000000
> 
> [  371.115916] Call trace:
> [  371.118439]  bcm_iproc_i2c_isr+0x530/0x11f0
> [  371.122754]  __handle_irq_event_percpu+0x6c/0x170
> [  371.127606]  handle_irq_event_percpu+0x34/0x88
> [  371.132189]  handle_irq_event+0x40/0x120
> [  371.136234]  handle_fasteoi_irq+0xcc/0x1a0
> [  371.140459]  generic_handle_irq+0x24/0x38
> [  371.144594]  __handle_domain_irq+0x60/0xb8
> [  371.148820]  gic_handle_irq+0xc0/0x158
> [  371.152687]  el1_irq+0xb8/0x140
> [  371.155927]  arch_cpu_idle+0x10/0x18
> [  371.159615]  do_idle+0x204/0x290
> [  371.162943]  cpu_startup_entry+0x24/0x60
> [  371.166990]  rest_init+0xb0/0xbc
> [  371.170322]  arch_call_rest_init+0xc/0x14
> [  371.174458]  start_kernel+0x404/0x430
> 
> Fixes: c245d94ed106 ("i2c: iproc: Add multi byte read-write support for slave mode")
> Signed-off-by: Dhananjay Phadke <dphadke@linux.microsoft.com>
> ---
>  drivers/i2c/busses/i2c-bcm-iproc.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-bcm-iproc.c b/drivers/i2c/busses/i2c-bcm-iproc.c
> index b58224b7b..37d2a79e7 100644
> --- a/drivers/i2c/busses/i2c-bcm-iproc.c
> +++ b/drivers/i2c/busses/i2c-bcm-iproc.c
> @@ -1074,14 +1074,15 @@ static int bcm_iproc_i2c_unreg_slave(struct i2c_client *slave)
>  	if (!iproc_i2c->slave)
>  		return -EINVAL;
>  
> -	iproc_i2c->slave = NULL;
> -
>  	/* disable all slave interrupts */
>  	tmp = iproc_i2c_rd_reg(iproc_i2c, IE_OFFSET);
>  	tmp &= ~(IE_S_ALL_INTERRUPT_MASK <<
>  			IE_S_ALL_INTERRUPT_SHIFT);
>  	iproc_i2c_wr_reg(iproc_i2c, IE_OFFSET, tmp);
>  
> +	synchronize_irq(iproc_i2c->irq);

If one takes a look at the I2C slave ISR routine, there are places where
IRQ can be re-enabled in the ISR itself. What happens after we mask all
slave interrupt and when 'synchronize_irq' is called, which I suppose is
meant to wait for inflight interrupt to finish where there's a chance
the interrupt can be re-enable again? How is one supposed to deal with that?

Thanks,

Ray

> +	iproc_i2c->slave = NULL;
> +
>  	/* Erase the slave address programmed */
>  	tmp = iproc_i2c_rd_reg(iproc_i2c, S_CFG_SMBUS_ADDR_OFFSET);
>  	tmp &= ~BIT(S_CFG_EN_NIC_SMB_ADDR3_SHIFT);
>