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    Subject[PATCH -rcu/kcsan 08/23] kcsan: Show location access was reordered to
    From
    Also show the location the access was reordered to. An example report:

    | ==================================================================
    | BUG: KCSAN: data-race in test_kernel_wrong_memorder / test_kernel_wrong_memorder
    |
    | read-write to 0xffffffffc01e61a8 of 8 bytes by task 2311 on cpu 5:
    | test_kernel_wrong_memorder+0x57/0x90
    | access_thread+0x99/0xe0
    | kthread+0x2ba/0x2f0
    | ret_from_fork+0x22/0x30
    |
    | read-write (reordered) to 0xffffffffc01e61a8 of 8 bytes by task 2310 on cpu 7:
    | test_kernel_wrong_memorder+0x57/0x90
    | access_thread+0x99/0xe0
    | kthread+0x2ba/0x2f0
    | ret_from_fork+0x22/0x30
    | |
    | +-> reordered to: test_kernel_wrong_memorder+0x80/0x90
    |
    | Reported by Kernel Concurrency Sanitizer on:
    | CPU: 7 PID: 2310 Comm: access_thread Not tainted 5.14.0-rc1+ #18
    | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
    | ==================================================================

    Signed-off-by: Marco Elver <elver@google.com>
    ---
    kernel/kcsan/report.c | 35 +++++++++++++++++++++++------------
    1 file changed, 23 insertions(+), 12 deletions(-)

    diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
    index 1b0e050bdf6a..67794404042a 100644
    --- a/kernel/kcsan/report.c
    +++ b/kernel/kcsan/report.c
    @@ -308,10 +308,12 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries

    /*
    * Skips to the first entry that matches the function of @ip, and then replaces
    - * that entry with @ip, returning the entries to skip.
    + * that entry with @ip, returning the entries to skip with @replaced containing
    + * the replaced entry.
    */
    static int
    -replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned long ip)
    +replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned long ip,
    + unsigned long *replaced)
    {
    unsigned long symbolsize, offset;
    unsigned long target_func;
    @@ -330,6 +332,7 @@ replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned lon
    func -= offset;

    if (func == target_func) {
    + *replaced = stack_entries[skip];
    stack_entries[skip] = ip;
    return skip;
    }
    @@ -342,9 +345,10 @@ replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned lon
    }

    static int
    -sanitize_stack_entries(unsigned long stack_entries[], int num_entries, unsigned long ip)
    +sanitize_stack_entries(unsigned long stack_entries[], int num_entries, unsigned long ip,
    + unsigned long *replaced)
    {
    - return ip ? replace_stack_entry(stack_entries, num_entries, ip) :
    + return ip ? replace_stack_entry(stack_entries, num_entries, ip, replaced) :
    get_stack_skipnr(stack_entries, num_entries);
    }

    @@ -360,6 +364,14 @@ static int sym_strcmp(void *addr1, void *addr2)
    return strncmp(buf1, buf2, sizeof(buf1));
    }

    +static void
    +print_stack_trace(unsigned long stack_entries[], int num_entries, unsigned long reordered_to)
    +{
    + stack_trace_print(stack_entries, num_entries, 0);
    + if (reordered_to)
    + pr_err(" |\n +-> reordered to: %pS\n", (void *)reordered_to);
    +}
    +
    static void print_verbose_info(struct task_struct *task)
    {
    if (!task)
    @@ -378,10 +390,12 @@ static void print_report(enum kcsan_value_change value_change,
    struct other_info *other_info,
    u64 old, u64 new, u64 mask)
    {
    + unsigned long reordered_to = 0;
    unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
    int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1);
    - int skipnr = sanitize_stack_entries(stack_entries, num_stack_entries, ai->ip);
    + int skipnr = sanitize_stack_entries(stack_entries, num_stack_entries, ai->ip, &reordered_to);
    unsigned long this_frame = stack_entries[skipnr];
    + unsigned long other_reordered_to = 0;
    unsigned long other_frame = 0;
    int other_skipnr = 0; /* silence uninit warnings */

    @@ -394,7 +408,7 @@ static void print_report(enum kcsan_value_change value_change,
    if (other_info) {
    other_skipnr = sanitize_stack_entries(other_info->stack_entries,
    other_info->num_stack_entries,
    - other_info->ai.ip);
    + other_info->ai.ip, &other_reordered_to);
    other_frame = other_info->stack_entries[other_skipnr];

    /* @value_change is only known for the other thread */
    @@ -434,10 +448,9 @@ static void print_report(enum kcsan_value_change value_change,
    other_info->ai.cpu_id);

    /* Print the other thread's stack trace. */
    - stack_trace_print(other_info->stack_entries + other_skipnr,
    + print_stack_trace(other_info->stack_entries + other_skipnr,
    other_info->num_stack_entries - other_skipnr,
    - 0);
    -
    + other_reordered_to);
    if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
    print_verbose_info(other_info->task);

    @@ -451,9 +464,7 @@ static void print_report(enum kcsan_value_change value_change,
    get_thread_desc(ai->task_pid), ai->cpu_id);
    }
    /* Print stack trace of this thread. */
    - stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
    - 0);
    -
    + print_stack_trace(stack_entries + skipnr, num_stack_entries - skipnr, reordered_to);
    if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
    print_verbose_info(current);

    --
    2.33.0.800.g4c38ced690-goog
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