Ben Greear <greearb@xxxxxxxxxxxxxxx> writes: > On 12/9/20 1:24 AM, Kalle Valo wrote: >> Wen Gong <wgong@xxxxxxxxxxxxxx> writes: >> >>> On 2020-09-08 00:22, Kalle Valo wrote: >>> >>>> Just like with the recent firmware restart patch, isn't >>>> ar->napi_enabled >>>> racy? Wouldn't test_and_set_bit() and test_and_clear_bit() be safer? >>>> >>>> Or are we holding a lock? But then that should be documented with >>>> lockdep_assert_held(). >>> >>> yes, ath10k_hif_start is only called from ath10k_core_start, it has >>> "lockdep_assert_held(&ar->conf_mutex)", and ath10k_hif_stop is only >>> called from ath10k_core_stop, it also has >>> "lockdep_assert_held(&ar->conf_mutex)". then it will not 2 thread both >>> enter ath10k_hif_start/ath10k_hif_stop meanwhile. >> >> Ok, but every function depending on a lock being held should still call >> lockdep_assert_held(), that way we can catch the bug if locking changes >> later. So it's not enough that ath10k_core_stop() has >> lockdep_assert_held(), also these napi functions should have it. >> >> I actually decided to switch using ATH10K_FLAG_NAPI_ENABLED with >> set_bit() & co, simpler locking that way and no lockdep_assert_held() >> needed anymore. Please check my changes in the pending branch, I have >> only compile tested them: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=e0a466d296bd862080f7796b41349f9f586272c9 >> > > Why do you not need locking? You can't just check a bit is set and > then do work and set it later without locking, two concurrent CPU > threads can pass the first check and both get into the logic below it? Good point, there is a race. I now fixed the patch in the pending and documented that core_mutex needs to be held when changing the NAPI state: https://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git/commit/?h=pending&id=2fe769592ef6d4ae14260989dcbdbde4bff01cb6 -- https://patchwork.kernel.org/project/linux-wireless/list/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
