Re: [PATCH] i2c: iproc: fix race between client unreg and tasklet

[Ray Jui]

On 8/5/2021 2:49 PM, Dhananjay Phadke wrote:
> Similar NULL deref was originally fixed by graceful teardown sequence -
> 
> https://lore.kernel.org/linux-i2c/1597106560-79693-1-git-send-email-dphadke@xxxxxxxxxxxxxxxxxxx
> 
> After this, a tasklet was added to take care of FIFO full condition for large i2c
> transaction.
> 
> https://lore.kernel.org/linux-arm-kernel/20201102035433.6774-1-rayagonda.kokatanur@xxxxxxxxxxxx/
> 
> This introduced regression, a new race condition between tasklet enabling
> interrupts and client unreg teardown sequence.
> 
> Kill tasklet before unreg_slave() masks bits in IE_OFFSET.
> Updated teardown sequence -
> (1) disable_irq()
> (2) Kill tasklet
> (3) Mask event enable bits in control reg
> (4) Erase slave address (avoid further writes to rx fifo)
> (5) Flush tx and rx FIFOs
> (6) Clear pending event (interrupt) bits in status reg
> (7) Set client pointer to NULL
> (8) enable_irq()
> 
>  --
> 
>  Unable to handle kernel read from unreadable memory at virtual address 0000000000000320
>  Mem abort info:
>    ESR = 0x96000004
>    EC = 0x25: DABT (current EL), IL = 32 bits
>    SET = 0, FnV = 0
>    EA = 0, S1PTW = 0
>  Data abort info:
>    ISV = 0, ISS = 0x00000004
>    CM = 0, WnR = 0
>  user pgtable: 4k pages, 48-bit VAs, pgdp=000000009212a000
>  [0000000000000320] pgd=0000000000000000, p4d=0000000000000000
>  Internal error: Oops: 96000004 [#1] SMP
>  CPU: 0 PID: 0 Comm: swapper/0 Tainted: G           O
>  Hardware name: Overlake (DT)
>  pstate: 40400085 (nZcv daIf +PAN -UAO -TCO BTYPE=--)
>  pc : bcm_iproc_i2c_slave_isr+0x2b8/0x8e4
>  lr : bcm_iproc_i2c_slave_isr+0x1c8/0x8e4
>  sp : ffff800010003e70
>  x29: ffff800010003e80 x28: ffffda017acdc000
>  x27: ffffda017b0ae000 x26: ffff800010004000
>  x25: ffff800010000000 x24: ffffda017af4a168
>  x23: 0000000000000073 x22: 0000000000000000
>  x21: 0000000001400000 x20: 0000000001000000
>  x19: ffff06f09583f880 x18: 00000000fa83b2da
>  x17: 000000000000b67e x16: 0000000002edb2f3
>  x15: 00000000000002c7 x14: 00000000000002c7
>  x13: 0000000000000006 x12: 0000000000000033
>  x11: 0000000000000000 x10: 0000000001000000
>  x9 : 0000000003289312 x8 : 0000000003289311
>  x7 : 02d0cd03a303adbc x6 : 02d18e7f0a4dfc6c
>  x5 : 02edb2f33f76ea68 x4 : 00000000fa83b2da
>  x3 : ffffda017af43cd0 x2 : ffff800010003e74
>  x1 : 0000000001400000 x0 : 0000000000000000
>  Call trace:
>   bcm_iproc_i2c_slave_isr+0x2b8/0x8e4
>   bcm_iproc_i2c_isr+0x178/0x290
>   __handle_irq_event_percpu+0xd0/0x200
>   handle_irq_event+0x60/0x1a0
>   handle_fasteoi_irq+0x130/0x220
>   __handle_domain_irq+0x8c/0xcc
>   gic_handle_irq+0xc0/0x120
>   el1_irq+0xcc/0x180
>   finish_task_switch+0x100/0x1d8
>   __schedule+0x61c/0x7a0
>   schedule_idle+0x28/0x44
>   do_idle+0x254/0x28c
>   cpu_startup_entry+0x28/0x2c
>   rest_init+0xc4/0xd0
>   arch_call_rest_init+0x14/0x1c
>   start_kernel+0x33c/0x3b8
>  Code: f9423260 910013e2 11000509 b9047a69 (f9419009)
>  ---[ end trace 4781455b2a7bec15 ]---
> 
> Fixes: 4d658451c9d6 ("i2c: iproc: handle rx fifo full interrupt")
> 
> Signed-off-by: Dhananjay Phadke <dphadke@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/i2c/busses/i2c-bcm-iproc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-bcm-iproc.c b/drivers/i2c/busses/i2c-bcm-iproc.c
> index cceaf69279a9..6304d1dd2dd6 100644
> --- a/drivers/i2c/busses/i2c-bcm-iproc.c
> +++ b/drivers/i2c/busses/i2c-bcm-iproc.c
> @@ -1224,14 +1224,14 @@ static int bcm_iproc_i2c_unreg_slave(struct i2c_client *slave)
>  
>  	disable_irq(iproc_i2c->irq);
>  
> +	tasklet_kill(&iproc_i2c->slave_rx_tasklet);
> +
>  	/* 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);
>  
> -	tasklet_kill(&iproc_i2c->slave_rx_tasklet);
> -
>  	/* 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);
> 

Yeah, needs to ensure no pending tasklet running to enable (unmask)
slave interrupts before disable (mask) them.

Thanks for the fix!

Acked-by: Ray Jui <ray.jui@xxxxxxxxxxxx>

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