On Thu, 30 Jul 2026 12:30:10 +0200 Peter Zijlstra <[email protected]> wrote:
> On Thu, Jul 30, 2026 at 10:45:39AM +0900, Masami Hiramatsu (Google) wrote: > > From: Masami Hiramatsu (Google) <[email protected]> > > > > find_active_uprobe_speculative() is called from find_active_uprobe_rcu(), > > which is invoked by handle_swbp() and handle_syscall_uprobe(). > > Both callers already hold RCU Tasks Trace (via rcu_read_lock_trace() or > > guard(rcu_tasks_trace)()). > > > > Calling guard(rcu)() inside find_active_uprobe_speculative() is redundant > > because the caller already guarantees RCU Tasks Trace protection. > > Furthermore, standard RCU (rcu_read_lock()) does not protect uprobes_tree > > against asynchronous uprobe destruction (call_rcu_tasks_trace()). > > > > Remove the redundant guard(rcu)() from find_active_uprobe_speculative() and > > replace it with lockdep_assert(rcu_read_lock_trace_held()) and a comment > > documenting that callers must hold RCU Tasks Trace protection, matching the > > convention used by find_active_uprobe_rcu() and find_uprobe_rcu(). > > > > Fixes: e0925f2dc4de ("uprobes: add speculative lockless > > VMA-to-inode-to-uprobe resolution") > > Assisted-by: Antigravity:gemini-3.6-flash > > Signed-off-by: Masami Hiramatsu (Google) <[email protected]> > > --- > > kernel/events/uprobes.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > index 4084e926e284..b4e253d43b30 100644 > > --- a/kernel/events/uprobes.c > > +++ b/kernel/events/uprobes.c > > @@ -2424,6 +2424,7 @@ static int is_trap_at_addr(struct mm_struct *mm, > > unsigned long vaddr) > > return is_trap_insn(&opcode); > > } > > > > +/* assumes being inside RCU Tasks Trace protected region */ > > static struct uprobe *find_active_uprobe_speculative(unsigned long > > bp_vaddr) > > { > > struct mm_struct *mm = current->mm; > > @@ -2433,7 +2434,7 @@ static struct uprobe > > *find_active_uprobe_speculative(unsigned long bp_vaddr) > > loff_t offset; > > unsigned int seq; > > > > - guard(rcu)(); > > + lockdep_assert(rcu_read_lock_trace_held()); > > > > if (!mmap_lock_speculate_try_begin(mm, &seq)) > > return NULL; > > Seems fine, but it this really worthy of Fixes? I mean, its just a micro > optimization, no? Yeah, I agree this is a kind of cleanup. But Sashiko pointed that this guard(rcu)() is for protecting vma/vm_file access. Maybe what we need is to add a comment that this guard(rcu)() is for protecting vma during this operation. (mmap_lock_speculate_try_begin() only checks a sequence number, not locking.) Thank you, -- Masami Hiramatsu (Google) <[email protected]>
