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Date:   Fri, 7 Aug 2020 17:35:49 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Dhananjay Phadke <dphadke@...ux.microsoft.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wolfram Sang <wsa@...nel.org>, Ray Jui <rjui@...adcom.com>
Cc:     Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2] i2c: iproc: fix race between client unreg and isr



On 8/7/2020 3:02 PM, Dhananjay Phadke wrote:
> When i2c client unregisters, synchronize irq before setting
> iproc_i2c->slave to NULL.
> 
> (1) disable_irq()
> (2) Mask event enable bits in control reg
> (3) Erase slave address (avoid further writes to rx fifo)
> (4) Flush tx and rx FIFOs
> (5) Clear pending event (interrupt) bits in status reg
> (6) enable_irq()
> (7) Set client pointer 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@...ux.microsoft.com>
> ---
>  drivers/i2c/busses/i2c-bcm-iproc.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-bcm-iproc.c b/drivers/i2c/busses/i2c-bcm-iproc.c
> index 8a3c98866fb7..c576776ffb10 100644
> --- a/drivers/i2c/busses/i2c-bcm-iproc.c
> +++ b/drivers/i2c/busses/i2c-bcm-iproc.c
> @@ -1078,7 +1078,7 @@ static int bcm_iproc_i2c_unreg_slave(struct i2c_client *slave)
>  	if (!iproc_i2c->slave)
>  		return -EINVAL;
>  
> -	iproc_i2c->slave = NULL;
> +	disable_irq(iproc_i2c->irq);
>  
>  	/* disable all slave interrupts */
>  	tmp = iproc_i2c_rd_reg(iproc_i2c, IE_OFFSET);
> @@ -1091,6 +1091,17 @@ static int bcm_iproc_i2c_unreg_slave(struct i2c_client *slave)
>  	tmp &= ~BIT(S_CFG_EN_NIC_SMB_ADDR3_SHIFT);
>  	iproc_i2c_wr_reg(iproc_i2c, S_CFG_SMBUS_ADDR_OFFSET, tmp);
>  
> +	/* flush TX/RX FIFOs */
> +	tmp = (BIT(S_FIFO_RX_FLUSH_SHIFT) | BIT(S_FIFO_TX_FLUSH_SHIFT));
> +	iproc_i2c_wr_reg(iproc_i2c, S_FIFO_CTRL_OFFSET, tmp);
> +
> +	/* clear all pending slave interrupts */
> +	iproc_i2c_wr_reg(iproc_i2c, IS_OFFSET, ISR_MASK_SLAVE);
> +
> +	enable_irq(iproc_i2c->irq);
> +
> +	iproc_i2c->slave = NULL;

There is nothing that checks on iproc_i2c->slave being valid within the
interrupt handler, we assume that the pointer is valid which is fin,
however non functional it may be, it may feel more natural to move the
assignment before the enable_irq()?
-- 
Florian

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