Thanks for your reply.
On 2022/1/11 6:03 pm, Karsten Graul wrote:
On 10/01/2022 10:38, Wen Gu wrote:
We encountered a crash in smc_setsockopt() and it is caused by
accessing smc->clcsock after clcsock was released.
In the switch() the function smc_switch_to_fallback() might be called which also
accesses smc->clcsock without further checking. This should also be protected then?
Also from all callers of smc_switch_to_fallback() ?
There are more uses of smc->clcsock (e.g. smc_bind(), ...), so why does this problem
happen in setsockopt() for you only? I suspect it depends on the test case.
Yes, it depends on the test case. The crash described here only happens one time when
I run a stress test of nginx/wrk, accompanied with frequent RNIC up/down operations.
Considering accessing smc->clcsock after its release is an uncommon, low probability
issue and only happens in setsockopt() in my test, I choce an simple way to fix it, using
the existing clcsock_release_lock, and only check in smc_setsockopt() and smc_getsockopt().
I wonder if it makes sense to check and protect smc->clcsock at all places in the code where
it is used... as of now we had no such races like you encountered. But I see that in theory
this problem could also happen in other code areas.
But inspired by your questions, I think maybe we should treat the race as a general problem?
Do you think it is necessary to find all the potential race related to the clcsock release and
fix them in a unified approach? like define smc->clcsock as RCU pointer, hold rcu read lock
before accessing smc->clcsock and call synchronize_rcu() before resetting smc->clcsock? just a rough idea :)
Or we should decide it later, do some more tests to see the probability of recurrence of this problem?
Thanks,
Wen Gu
