On 2022-08-21 11:32:21 [+0800], Hou Tao wrote: > process A process B > > htab_map_update_elem() > htab_lock_bucket() > migrate_disable() > /* return 1 */ > __this_cpu_inc_return() > /* preempted by B */ > > htab_map_update_elem() > /* the same bucket as A */ > htab_lock_bucket() > migrate_disable() > /* return 2, so lock fails */ > __this_cpu_inc_return() > return -EBUSY > > A fix that seems feasible is using in_nmi() in htab_lock_bucket() and > only checking the value of map_locked for nmi context. But it will > re-introduce dead-lock on bucket lock if htab_lock_bucket() is re-entered > through non-tracing program (e.g. fentry program). > > So fixing it by using disable_preempt() instead of migrate_disable() when > increasing htab->map_locked. However when htab_use_raw_lock() is false, > bucket lock will be a sleepable spin-lock and it breaks disable_preempt(), > so still use migrate_disable() for spin-lock case. But isn't the RT case still affected by the very same problem? > Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx> Sebastian
