On 3/10/22 23:47, Jim Cromie wrote: > In https://urldefense.com/v3/__https://lore.kernel.org/lkml/20211209150910.GA23668@xxxxxxxx/__;!!GjvTz_vk!HGKKoni4RVdEBgv_V0zPSNSX428bpf02zkCy2WbeQkBdVtp1QJqGX-lJYlRDGg$ > > Vincent's patch commented on, and worked around, a bug toggling > static_branch's, when a 2nd PRINTK-ish flag was added. The bug > results in a premature static_branch_disable when the 1st of 2 flags > was disabled. > > The cited commit computed newflags, but then in the JUMP_LABEL block, > failed to use that result, instead using just one of the terms in it. > Using newflags instead made the code work properly. > > This is Vincents test-case, reduced. It needs the 2nd flag to work > properly, but it's explanatory here. > > pt_test() { > echo 5 > /sys/module/dynamic_debug/verbose > > site="module tcp" # just one callsite > echo " $site =_ " > /proc/dynamic_debug/control # clear it > > # A B ~A ~B > for flg in +T +p "-T #broke here" -p; do > echo " $site $flg " > /proc/dynamic_debug/control > done; > > # A B ~B ~A > for flg in +T +p "-p #broke here" -T; do > echo " $site $flg " > /proc/dynamic_debug/control > done > } > pt_test > > Fixes: 84da83a6ffc0 dyndbg: combine flags & mask into a struct, simplify with it > CC: vincent.whitchurch@xxxxxxxx > Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx> > > -- > .drop @stable, no exposed bug. > --- > lib/dynamic_debug.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c > index dd7f56af9aed..a56c1286ffa4 100644 > --- a/lib/dynamic_debug.c > +++ b/lib/dynamic_debug.c > @@ -211,10 +211,11 @@ static int ddebug_change(const struct ddebug_query *query, > continue; > #ifdef CONFIG_JUMP_LABEL > if (dp->flags & _DPRINTK_FLAGS_PRINT) { > - if (!(modifiers->flags & _DPRINTK_FLAGS_PRINT)) > + if (!(newflags & _DPRINTK_FLAGS_PRINT)) > static_branch_disable(&dp->key.dd_key_true); > - } else if (modifiers->flags & _DPRINTK_FLAGS_PRINT) > + } else if (newflags & _DPRINTK_FLAGS_PRINT) { > static_branch_enable(&dp->key.dd_key_true); > + } > #endif > dp->flags = newflags; > v4pr_info("changed %s:%d [%s]%s =%s\n", Hi Jim, If iiuc this is currently a bug but could be if we add a second 'print' bit such as for printing to the tracing logs. That said I agree that using 'newflags' here makes the code more straightforward/readable. So this one is fine with me. Acked-by: Jason Baron <jbaron@xxxxxxxxxx> Thanks, -Jason
