On 3/10/22 23:47, Jim Cromie wrote:
> In
> https://urldefense.com/v3/__https://lore.kernel.org/lkml/20211209150910.ga23...@axis.com/__;!!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.whitchu...@axis.com
> Signed-off-by: Jim Cromie <jim.cro...@gmail.com>
>
> --
> .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 <jba...@akamai.com>
Thanks,
-Jason
