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[73.78.62.130]) by smtp.googlemail.com with ESMTPSA id n9-20020a056638110900b003435e8635bbsm27928jal.77.2022.08.11.10.35.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Aug 2022 10:35:52 -0700 (PDT) From: Jim Cromie To: linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, jbaron@akamai.com Cc: Jim Cromie , vincent.whitchurch@axis.com Subject: [PATCH 01/11] dyndbg: fix static_branch manipulation Date: Thu, 11 Aug 2022 11:35:31 -0600 Message-Id: <20220811173541.2901122-2-jim.cromie@gmail.com> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220811173541.2901122-1-jim.cromie@gmail.com> References: <20220811173541.2901122-1-jim.cromie@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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=3D"module tcp" # just one callsite echo " $site =3D_ " > /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 wi= th it CC: vincent.whitchurch@axis.com Signed-off-by: Jim Cromie Acked-by: Jason Baron --- .drop @stable, no exposed bug. .add jbaron ack --- 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 *q= uery, 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 =3D newflags; v4pr_info("changed %s:%d [%s]%s =3D%s\n", --=20 2.37.1