On Fri, Jul 26, 2024 at 03:48:45PM -0700, Song Liu wrote: > On Fri, Jul 26, 2024 at 2:49 PM Matt Bobrowski <mattbobrowski@xxxxxxxxxx> wrote: > > > > On Fri, Jul 26, 2024 at 02:25:26PM -0700, Song Liu wrote: > > > On Fri, Jul 26, 2024 at 1:56 AM Matt Bobrowski <mattbobrowski@xxxxxxxxxx> wrote: > > > > > > > [...] > > > > + len = buf + buf__sz - ret; > > > > + memmove(buf, ret, len); > > > > + return len; > > > > +} > > > > +__bpf_kfunc_end_defs(); > > > > + > > > > +BTF_KFUNCS_START(bpf_fs_kfunc_set_ids) > > > > +BTF_ID_FLAGS(func, bpf_get_task_exe_file, > > > > + KF_ACQUIRE | KF_TRUSTED_ARGS | KF_SLEEPABLE | KF_RET_NULL) > > > > +BTF_ID_FLAGS(func, bpf_put_file, KF_RELEASE | KF_SLEEPABLE) > > > > > > Do we really need KF_SLEEPABLE for bpf_put_file? > > > > Well, the guts of fput() is annotated w/ might_sleep(), so the calling > > thread may presumably be involuntarily put to sleep? You can also see > > the guts of fput() invoking various indirect function calls > > i.e. ->release(), and depending on the implementation of those, they > > could be initiating resource release related actions which > > consequently could result in waiting for some I/O to be done? fput() > > also calls dput() and mntput() and these too can also do a bunch of > > teardown. > > > > Please correct me if I've misunderstood something. > > __fput() is annotated with might_sleep(). However, fput() doesn't not > call __fput() directly. Instead, it schedules a worker to call __fput(). > Therefore, it is safe to call fput() from a non-sleepable context. Oh, yes, you're absolutely right. I failed to realize that, so my apologies. In that case, yes, technically bpf_put_file() does not need to be annotated w/ KF_SLEEPABLE. Now that I also think of it, one of the other and only reasons why we made this initially sleepable is because bpf_put_file() at the time was meant to be used exclusively within the same context as bpf_path_d_path(), and that is currently marked as sleepable. Although technically speaking, I think we could also make bpf_path_d_path() not restricted to only sleepable BPF LSM program types, and in turn that could mean that bpf_get_task_exe_file() also doesn't need to be restricted to sleepable BPF LSM programs. Alexei, what do you think about relaxing the sleepable annotation across this entire set of BPF kfuncs? From a technical perspective I think it's OK, but I'd also like someone like Christian to confirm that d_path() can't actually end up sleeping. Glancing over it, I believe this to be true, but I may also be naively missing something. /M
