On Wed, 2024-08-14 at 11:54 -0700, Andrii Nakryiko wrote: > Add sleepable implementations of bpf_get_stack() and > bpf_get_task_stack() helpers and allow them to be used from sleepable > BPF program (e.g., sleepable uprobes). > > Note, the stack trace IPs capturing itself is not sleepable (that would > need to be a separate project), only build ID fetching is sleepable and > thus more reliable, as it will wait for data to be paged in, if > necessary. For that we make use of sleepable build_id_parse() > implementation. > > Now that build ID related internals in kernel/bpf/stackmap.c can be used > both in sleepable and non-sleepable contexts, we need to add additional > rcu_read_lock()/rcu_read_unlock() protection around fetching > perf_callchain_entry, but with the refactoring in previous commit it's > now pretty straightforward. We make sure to do rcu_read_unlock (in > sleepable mode only) right before stack_map_get_build_id_offset() call > which can sleep. By that time we don't have any more use of > perf_callchain_entry. > > Note, bpf_get_task_stack() will fail for user mode if task != current. > And for kernel mode build ID are irrelevant. So in that sense adding > sleepable bpf_get_task_stack() implementation is a no-op. It feel right > to wire this up for symmetry and completeness, but I'm open to just > dropping it until we support `user && crosstask` condition. > > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > --- All seems logical. You skip wiring up support for sleepable bpf_get_task_stack() in tp_prog_func_proto(), pe_prog_func_proto() and raw_tp_prog_func_proto(), this is because these are used for programs that are never run in sleepable context, right? Reviewed-by: Eduard Zingerman <eddyz87@xxxxxxxxx> [...]
