dyndbg: fix static_branch manipulation

[ Upstream commit ee879be38bc87f8cedc79ae2742958db6533ca59 ]

In https://lore.kernel.org/lkml/20211209150910.GA23668@axis.com/

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
demonstrate the bug, 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@axis.com
Acked-by: Jason Baron <jbaron@akamai.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20220904214134.408619-2-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 84c16309cc63789b4b3dec4af26576e07935e9f6..00e6507972d8aaafc3b446f2eb7648b0285ec733 100644 (file)
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -207,10 +207,11 @@ 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;
                        v2pr_info("changed %s:%d [%s]%s =%s\n",