Re: Segmentation fault when taking device for a walk

[James Prestwood <prestwoj@gmail.com>]

Hi Richard,

On 8/15/24 5:24 PM, Richard Acayan wrote:
> Hi,
>
> A segmentation fault occurs in station_start_roam() when the station is
> disconnected from an access point, or in other words, when the station's
> connected_bss is NULL. Usually, this is triggered by a timeout, possibly
> scheduled in response to a weak signal event.
>
> This is occurring on my Pixel 3a running postmarketOS/Alpine Linux, when
> receding from an access point, on iwd 2.19. I have collected 6 coredumps
> of the crash in the span of around 2 weeks and would be willing to use
> GDB if more information is necessary for a patch.
>
> Sample:
>
> 	Program terminated with signal SIGSEGV, Segmentation fault.
> 	#0  0x0000aaaadf2086a0 in station_start_roam (station=0xffff8776ae50) at src/station.c:2880
> 	
> 	warning: 2880	src/station.c: No such file or directory
> 	(gdb) bt
> 	#0  0x0000aaaadf2086a0 in station_start_roam (station=0xffff8776ae50) at src/station.c:2880
> 	#1  0x0000aaaadf28c544 in timeout_callback (fd=<optimized out>, events=<optimized out>,
> 	    user_data=0xffff876b2e20) at ell/timeout.c:68
> 	#2  timeout_callback (fd=<optimized out>, events=<optimized out>, user_data=0xffff876b2e20)
> 	    at ell/timeout.c:57
> 	#3  0x0000aaaadf28b9d0 in l_main_iterate (timeout=<optimized out>) at ell/main.c:461
> 	#4  0x0000aaaadf28bac0 in l_main_run () at ell/main.c:508
> 	#5  l_main_run () at ell/main.c:490
> 	#6  0x0000aaaadf28bce4 in l_main_run_with_signal (
> 	    callback=callback@entry=0xaaaadf1f1110 <signal_handler>, user_data=user_data@entry=0x0)
> 	    at ell/main.c:630
> 	#7  0x0000aaaadf1f0b0c in main (argc=<optimized out>, argv=<optimized out>) at src/main.c:611
> 	(gdb) p station->connected_bss
> 	$1 = (struct scan_bss *) 0x0
>
Its hard to say without any debug logs as well but it appears the 
disconnect never cleared out the timer used for the next roam attempt. I 
did fix a hang due to a disconnect coming in during a roam attempt after 
2.19, but I can't really make heads or tails without debug logs to see 
what happened before/after the disconnect.

Thanks,

James