On Thu, Jun 11, 2026 at 6:21 PM Yunseong Kim <[email protected]> wrote: > > The recursion guard (bit-31 of kcov_df_seq) prevents reentry when > copy_from_kernel_nofault() or other called functions are instrumented > with INSTRUMENT_ALL. Without compiler barriers, the guard set/clear > can be reordered relative to the function body, making the protection > ineffective under optimization. > > Add barrier() after setting the guard and before clearing it, ensuring > the compiler does not move instrumented operations outside the guarded > region. > > Cc: Peter Zijlstra <[email protected]> > Signed-off-by: Yunseong Kim <[email protected]> > --- > kernel/kcov_dataflow.c | 2 ++
Please merge this patch into the one introducing kcov_dataflow.c > 1 file changed, 2 insertions(+) > > diff --git a/kernel/kcov_dataflow.c b/kernel/kcov_dataflow.c > index df7e8bf70bfa..5248293280d5 100644 > --- a/kernel/kcov_dataflow.c > +++ b/kernel/kcov_dataflow.c > @@ -86,6 +86,7 @@ kcov_df_write(u64 type_marker, u64 pc, u64 meta, void *ptr, > if (t->kcov_df_seq & (1U << 31)) > return; > t->kcov_df_seq |= (1U << 31); > + barrier(); Please make sure barriers have comments explaining which barriers they pair with (see kernel/kcov.c)
