On Sat, 9 Dec 2023 13:20:09 +0100 Greg KH <greg@xxxxxxxxx> wrote: > On Wed, Dec 06, 2023 at 10:57:11AM +0900, mhiramat@xxxxxxxxxx wrote: > > From: JP Kobryn <inwardvessel@xxxxxxxxx> > > > > It seems that the pointer-to-kretprobe "rp" within the kretprobe_holder is > > RCU-managed, based on the (non-rethook) implementation of get_kretprobe(). > > The thought behind this patch is to make use of the RCU API where possible > > when accessing this pointer so that the needed barriers are always in place > > and to self-document the code. > > > > The __rcu annotation to "rp" allows for sparse RCU checking. Plain writes > > done to the "rp" pointer are changed to make use of the RCU macro for > > assignment. For the single read, the implementation of get_kretprobe() > > is simplified by making use of an RCU macro which accomplishes the same, > > but note that the log warning text will be more generic. > > > > I did find that there is a difference in assembly generated between the > > usage of the RCU macros vs without. For example, on arm64, when using > > rcu_assign_pointer(), the corresponding store instruction is a > > store-release (STLR) which has an implicit barrier. When normal assignment > > is done, a regular store (STR) is found. In the macro case, this seems to > > be a result of rcu_assign_pointer() using smp_store_release() when the > > value to write is not NULL. > > > > Link: https://lore.kernel.org/all/20231122132058.3359-1-inwardvessel@xxxxxxxxx/ > > > > Fixes: d741bf41d7c7 ("kprobes: Remove kretprobe hash") > > Cc: stable@xxxxxxxxxxxxxxx > > Signed-off-by: JP Kobryn <inwardvessel@xxxxxxxxx> > > Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> > > (cherry picked from commit d839a656d0f3caca9f96e9bf912fd394ac6a11bc) > > --- > > include/linux/kprobes.h | 8 +++----- > > kernel/kprobes.c | 4 ++-- > > 2 files changed, 5 insertions(+), 7 deletions(-) > > Did you build this? It breaks the build in 6.6.y in horrible ways: > > ./include/linux/kprobes.h:145:33: error: field ‘pool’ has incomplete type > 145 | struct objpool_head pool; > | ^~~~ > > > I'll drop this, can you please provide a working version? Oops, sorry. I missed to patch this version. Let me update it. > > thanks, > > greg k-h -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
