lkml.org 
[lkml]   [2022]   [Aug]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH v5 01/33] dyndbg: fix static_branch manipulation
    Date
    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
    Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
    Acked-by: Jason Baron <jbaron@akamai.com>
    ---
    .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 *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",
    --
    2.37.1
    \
     
     \ /
      Last update: 2022-08-05 23:55    [W:3.066 / U:0.500 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site