On 3/5/24 17:18, Christophe Leroy wrote: > > > Le 05/03/2024 à 19:14, Sean Anderson a écrit : >> [Vous ne recevez pas souvent de courriers de sean.anderson@xxxxxxxxx. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ] >> >> Hi, >> >> On 2/23/24 11:02, Sean Anderson wrote: >>> On 2/23/24 00:38, Christophe Leroy wrote: >>>> Le 22/02/2024 à 18:07, Sean Anderson a écrit : >>>>> [Vous ne recevez pas souvent de courriers de sean.anderson@xxxxxxxxx. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ] >>>>> >>>>> cgr_lock may be locked with interrupts already disabled by >>>>> smp_call_function_single. As such, we must use a raw spinlock to avoid >>>>> problems on PREEMPT_RT kernels. Although this bug has existed for a >>>>> while, it was not apparent until commit ef2a8d5478b9 ("net: dpaa: Adjust >>>>> queue depth on rate change") which invokes smp_call_function_single via >>>>> qman_update_cgr_safe every time a link goes up or down. >>>> >>>> Why a raw spinlock to avoid problems on PREEMPT_RT, can you elaborate ? >>> >>> smp_call_function always runs its callback in hard IRQ context, even on >>> PREEMPT_RT, where spinlocks can sleep. So we need to use raw spinlocks >>> to ensure we aren't waiting on a sleeping task. See the first bug report >>> for more discussion. >>> >>> In the longer term it would be better to switch to some other >>> abstraction. >> >> Does this make sense to you? > > Yes that fine, thanks for the clarification. Maybe you can explain that > in the patch description in case you send a v5. Hm, I thought I put this description in the commit message already. Maybe something like | smp_call_function always runs its callback in hard IRQ context, even on | PREEMPT_RT, where spinlocks can sleep. So we need to use a raw spinlock | for cgr_lock to ensure we aren't waiting on a sleeping task. | | Although this bug has existed for a while, it was not apparent until | commit ef2a8d5478b9 ("net: dpaa: Adjust queue depth on rate change") | which invokes smp_call_function_single via qman_update_cgr_safe every | time a link goes up or down. would be clearer. --Sean
