[dm-devel] [PATCH 2/4] multipath-tools: add checker callout to repair path

[Mike Christie]

On 08/11/2016 10:50 AM, Bart Van Assche wrote:
> On 08/08/2016 05:01 AM, Mike Christie wrote:
>> This patch adds a callback which can be used to repair a path
>> if check() has determined it is in the PATH_DOWN state.
>>
>> The next patch that adds rbd checker support which will use this to
>> handle the case where a rbd device is blacklisted.
> 
> Hello Mike,
> 
> With this patch applied, with the TUR checker enabled in multipath.conf
> I see the following crash if I trigger SRP failover and failback:
> 
> ion-dev-ib-ini:~ # gdb ~bart/software/multipath-tools/multipathd/multipathd
> (gdb) handle SIGPIPE noprint nostop
> Signal        Stop      Print   Pass to program Description
> SIGPIPE       No        No      Yes             Broken pipe
> (gdb) run -d
> Aug 11 08:46:27 | sde: remove path (uevent)
> Aug 11 08:46:27 | mpathbe: adding map
> Aug 11 08:46:27 | 8:64: cannot find block device
> Aug 11 08:46:27 | Invalid device number 1
> Aug 11 08:46:27 | 1: cannot find block device
> Aug 11 08:46:27 | 8:96: cannot find block device
> Aug 11 08:46:27 | mpathbe: failed to setup multipath
> Aug 11 08:46:27 | dm-0: uev_add_map failed
> Aug 11 08:46:27 | uevent trigger error
> 
> Thread 4 "multipathd" received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0x7ffff7f8b700 (LWP 8446)]
> 0x0000000000000000 in ?? ()
> (gdb) bt
> #0  0x0000000000000000 in ?? ()
> #1  0x00007ffff6c41905 in checker_repair (c=0x7fffdc001ef0) at checkers.c:225
> #2  0x000000000040a760 in repair_path (vecs=0x66d7e0, pp=0x7fffdc001a40)
>     at main.c:1733
> #3  0x000000000040ab27 in checkerloop (ap=0x66d7e0) at main.c:1807
> #4  0x00007ffff79bb474 in start_thread (arg=0x7ffff7f8b700)
>     at pthread_create.c:333
> #5  0x00007ffff63243ed in clone ()
>     at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
> (gdb) up
> #1  0x00007ffff6c41905 in checker_repair (c=0x7fffdc001ef0) at checkers.c:225
> 225             c->repair(c);
> (gdb) print *c
> $1 = {node = {next = 0x0, prev = 0x0}, handle = 0x0, refcount = 0, fd = 0, 
>   sync = 0, timeout = 0, disable = 0, name = '\000' <repeats 15 times>, 
>   message = '\000' <repeats 255 times>, context = 0x0, mpcontext = 0x0, 
>   check = 0x0, repair = 0x0, init = 0x0, free = 0x0}
> 

Sorry about the stupid bug.

Could you try the attached patch. I found two segfaults. If check_path
returns less than 0 then we free the path and so we cannot call repair
on it. If libcheck_init fails it memsets the checker, so we cannot call
repair on it too.

I moved the repair call to the specific paths that the path is down.
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