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    Subject[PATCH 2/9] kcsan: Distinguish kcsan_report() calls
    From
    From: Mark Rutland <mark.rutland@arm.com>

    Currently kcsan_report() is used to handle three distinct cases:

    * The caller hit a watchpoint when attempting an access. Some
    information regarding the caller and access are recorded, but no
    output is produced.

    * A caller which previously setup a watchpoint detected that the
    watchpoint has been hit, and possibly detected a change to the
    location in memory being watched. This may result in output reporting
    the interaction between this caller and the caller which hit the
    watchpoint.

    * A caller detected a change to a modification to a memory location
    which wasn't detected by a watchpoint, for which there is no
    information on the other thread. This may result in output reporting
    the unexpected change.

    ... depending on the specific case the caller has distinct pieces of
    information available, but the prototype of kcsan_report() has to handle
    all three cases. This means that in some cases we pass redundant
    information, and in others we don't pass all the information we could
    pass. This also means that the report code has to demux these three
    cases.

    So that we can pass some additional information while also simplifying
    the callers and report code, add separate kcsan_report_*() functions for
    the distinct cases, updating callers accordingly. As the watchpoint_idx
    is unused in the case of kcsan_report_unknown_origin(), this passes a
    dummy value into kcsan_report(). Subsequent patches will refactor the
    report code to avoid this.

    There should be no functional change as a result of this patch.

    Signed-off-by: Mark Rutland <mark.rutland@arm.com>
    [ elver@google.com: try to make kcsan_report_*() names more descriptive ]
    Signed-off-by: Marco Elver <elver@google.com>
    ---
    kernel/kcsan/core.c | 12 ++++--------
    kernel/kcsan/kcsan.h | 10 ++++++----
    kernel/kcsan/report.c | 26 +++++++++++++++++++++++---
    3 files changed, 33 insertions(+), 15 deletions(-)

    diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
    index d360183002d6..6fe1513e1e6a 100644
    --- a/kernel/kcsan/core.c
    +++ b/kernel/kcsan/core.c
    @@ -380,9 +380,7 @@ static noinline void kcsan_found_watchpoint(const volatile void *ptr,

    if (consumed) {
    kcsan_save_irqtrace(current);
    - kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,
    - KCSAN_REPORT_CONSUMED_WATCHPOINT,
    - watchpoint - watchpoints);
    + kcsan_report_set_info(ptr, size, type, watchpoint - watchpoints);
    kcsan_restore_irqtrace(current);
    } else {
    /*
    @@ -558,8 +556,8 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
    if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
    atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);

    - kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL,
    - watchpoint - watchpoints);
    + kcsan_report_known_origin(ptr, size, type, value_change,
    + watchpoint - watchpoints);
    } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
    /* Inferring a race, since the value should not have changed. */

    @@ -568,9 +566,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
    atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);

    if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)
    - kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,
    - KCSAN_REPORT_RACE_UNKNOWN_ORIGIN,
    - watchpoint - watchpoints);
    + kcsan_report_unknown_origin(ptr, size, type);
    }

    /*
    diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
    index 9881099d4179..2ee43fd5d6a4 100644
    --- a/kernel/kcsan/kcsan.h
    +++ b/kernel/kcsan/kcsan.h
    @@ -136,10 +136,12 @@ enum kcsan_report_type {
    };

    /*
    - * Print a race report from thread that encountered the race.
    + * Notify the report code that a race occurred.
    */
    -extern void kcsan_report(const volatile void *ptr, size_t size, int access_type,
    - enum kcsan_value_change value_change,
    - enum kcsan_report_type type, int watchpoint_idx);
    +void kcsan_report_set_info(const volatile void *ptr, size_t size, int access_type,
    + int watchpoint_idx);
    +void kcsan_report_known_origin(const volatile void *ptr, size_t size, int access_type,
    + enum kcsan_value_change value_change, int watchpoint_idx);
    +void kcsan_report_unknown_origin(const volatile void *ptr, size_t size, int access_type);

    #endif /* _KERNEL_KCSAN_KCSAN_H */
    diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
    index 13dce3c664d6..5232bf218ea7 100644
    --- a/kernel/kcsan/report.c
    +++ b/kernel/kcsan/report.c
    @@ -598,9 +598,9 @@ static noinline bool prepare_report(unsigned long *flags,
    }
    }

    -void kcsan_report(const volatile void *ptr, size_t size, int access_type,
    - enum kcsan_value_change value_change,
    - enum kcsan_report_type type, int watchpoint_idx)
    +static void kcsan_report(const volatile void *ptr, size_t size, int access_type,
    + enum kcsan_value_change value_change,
    + enum kcsan_report_type type, int watchpoint_idx)
    {
    unsigned long flags = 0;
    const struct access_info ai = {
    @@ -645,3 +645,23 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type,
    out:
    kcsan_enable_current();
    }
    +
    +void kcsan_report_set_info(const volatile void *ptr, size_t size, int access_type,
    + int watchpoint_idx)
    +{
    + kcsan_report(ptr, size, access_type, KCSAN_VALUE_CHANGE_MAYBE,
    + KCSAN_REPORT_CONSUMED_WATCHPOINT, watchpoint_idx);
    +}
    +
    +void kcsan_report_known_origin(const volatile void *ptr, size_t size, int access_type,
    + enum kcsan_value_change value_change, int watchpoint_idx)
    +{
    + kcsan_report(ptr, size, access_type, value_change,
    + KCSAN_REPORT_RACE_SIGNAL, watchpoint_idx);
    +}
    +
    +void kcsan_report_unknown_origin(const volatile void *ptr, size_t size, int access_type)
    +{
    + kcsan_report(ptr, size, access_type, KCSAN_VALUE_CHANGE_TRUE,
    + KCSAN_REPORT_RACE_UNKNOWN_ORIGIN, 0);
    +}
    --
    2.31.1.295.g9ea45b61b8-goog
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