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? --Sean
