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From: Jim Cromie <jim.cromie@gmail.com>
To: jbaron@akamai.com, gregkh@linuxfoundation.org,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	amd-gfx@lists.freedesktop.org,
	intel-gvt-dev@lists.freedesktop.org,
	intel-gfx@lists.freedesktop.org
Cc: daniel.vetter@ffwll.ch, seanpaul@chromium.org,
	robdclark@gmail.com, linux@rasmusvillemoes.dk, joe@perches.com,
	Jim Cromie <jim.cromie@gmail.com>,
	vincent.whitchurch@axis.com, stable@vger.kernel.org
Subject: [PATCH 01/13] dyndbg: fix static_branch manipulation
Date: Wed, 16 Feb 2022 20:48:17 -0700	[thread overview]
Message-ID: <20220217034829.64395-2-jim.cromie@gmail.com> (raw)
In-Reply-To: <20220217034829.64395-1-jim.cromie@gmail.com>

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,
did not use that result, but used 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@axis.com
CC: stable@vger.kernel.org
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 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",
-- 
2.35.1


  reply	other threads:[~2022-02-17  3:48 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-17  3:48 [PATCH 00/12] use dynamic-debug under drm.debug api Jim Cromie
2022-02-17  3:48 ` Jim Cromie [this message]
2022-02-17  3:48 ` [PATCH 02/13] dyndbg: add class_id field and query support Jim Cromie
2022-02-17  3:48 ` [PATCH 03/13] dyndbg: add DEFINE_DYNAMIC_DEBUG_CLASSBITS macro and callbacks Jim Cromie
2022-02-17  3:48 ` [PATCH 04/13] dyndbg: drop EXPORTed dynamic_debug_exec_queries Jim Cromie
2022-02-17  3:48 ` [PATCH 05/13] dyndbg: improve change-info to have old and new Jim Cromie
2022-02-17  3:48 ` [PATCH 06/13] dyndbg: abstract dyndbg_site_is_printing Jim Cromie
2022-02-17  3:48 ` [PATCH 07/13] drm_print: condense enum drm_debug_category Jim Cromie
2022-02-17  3:48 ` [PATCH 08/13] drm_print: interpose drm_*dbg with forwarding macros Jim Cromie
2022-02-17  3:48 ` [PATCH 09/13] drm_print: wrap drm_*_dbg in dyndbg jumplabel Jim Cromie
2022-02-17  3:48 ` [PATCH 10/13] drm_print: refine drm_debug_enabled for dyndbg+jump-label Jim Cromie
2022-02-17  3:48 ` [PATCH 11/13] drm_print: prefer bare printk KERN_DEBUG on generic fn Jim Cromie
2022-02-17  3:48 ` [PATCH 12/13] drm_print: add _ddebug desc to drm_*dbg prototypes Jim Cromie
2022-02-17  3:48 ` [PATCH 13/13] drm_print: use DEFINE_DYNAMIC_DEBUG_CLASSBITS for drm.debug Jim Cromie
2022-03-01 16:46 [PATCH 00/12] use dynamic-debug under drm.debug api Jim Cromie
2022-03-01 16:46 ` [PATCH 01/13] dyndbg: fix static_branch manipulation Jim Cromie

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