Re: [PATCH v2 net 1/1] stmmac: fix potential division by 0

[Andrew Lunn <andrew@lunn.ch>]

On Sat, Dec 10, 2022 at 11:37:22PM +0100, Piergiorgio Beruto wrote:
> When the MAC is connected to a 10 Mb/s PHY and the PTP clock is derived
> from the MAC reference clock (default), the clk_ptp_rate becomes too
> small and the calculated sub second increment becomes 0 when computed by
> the stmmac_config_sub_second_increment() function within
> stmmac_init_tstamp_counter().
> 
> Therefore, the subsequent div_u64 in stmmac_init_tstamp_counter()
> operation triggers a divide by 0 exception as shown below.
> 
> [   95.062067] socfpga-dwmac ff700000.ethernet eth0: Register MEM_TYPE_PAGE_POOL RxQ-0
> [   95.076440] socfpga-dwmac ff700000.ethernet eth0: PHY [stmmac-0:08] driver [NCN26000] (irq=49)
> [   95.095964] dwmac1000: Master AXI performs any burst length
> [   95.101588] socfpga-dwmac ff700000.ethernet eth0: No Safety Features support found
> [   95.109428] Division by zero in kernel.
> [   95.113447] CPU: 0 PID: 239 Comm: ifconfig Not tainted 6.1.0-rc7-centurion3-1.0.3.0-01574-gb624218205b7-dirty #77
> [   95.123686] Hardware name: Altera SOCFPGA
> [   95.127695]  unwind_backtrace from show_stack+0x10/0x14
> [   95.132938]  show_stack from dump_stack_lvl+0x40/0x4c
> [   95.137992]  dump_stack_lvl from Ldiv0+0x8/0x10
> [   95.142527]  Ldiv0 from __aeabi_uidivmod+0x8/0x18
> [   95.147232]  __aeabi_uidivmod from div_u64_rem+0x1c/0x40
> [   95.152552]  div_u64_rem from stmmac_init_tstamp_counter+0xd0/0x164
> [   95.158826]  stmmac_init_tstamp_counter from stmmac_hw_setup+0x430/0xf00
> [   95.165533]  stmmac_hw_setup from __stmmac_open+0x214/0x2d4
> [   95.171117]  __stmmac_open from stmmac_open+0x30/0x44
> [   95.176182]  stmmac_open from __dev_open+0x11c/0x134
> [   95.181172]  __dev_open from __dev_change_flags+0x168/0x17c
> [   95.186750]  __dev_change_flags from dev_change_flags+0x14/0x50
> [   95.192662]  dev_change_flags from devinet_ioctl+0x2b4/0x604
> [   95.198321]  devinet_ioctl from inet_ioctl+0x1ec/0x214
> [   95.203462]  inet_ioctl from sock_ioctl+0x14c/0x3c4
> [   95.208354]  sock_ioctl from vfs_ioctl+0x20/0x38
> [   95.212984]  vfs_ioctl from sys_ioctl+0x250/0x844
> [   95.217691]  sys_ioctl from ret_fast_syscall+0x0/0x4c
> [   95.222743] Exception stack(0xd0ee1fa8 to 0xd0ee1ff0)
> [   95.227790] 1fa0:                   00574c4f be9aeca4 00000003 00008914 be9aeca4 be9aec50
> [   95.235945] 1fc0: 00574c4f be9aeca4 0059f078 00000036 be9aee8c be9aef7a 00000015 00000000
> [   95.244096] 1fe0: 005a01f0 be9aec38 004d7484 b6e67d74
> 
> Signed-off-by: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
> Fixes: 91a2559c1dc5 ("net: stmmac: Fix sub-second increment")

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew