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kcsan: Address missing case with KCSAN_REPORT_VALUE_CHANGE_ONLY 

Even with KCSAN_REPORT_VALUE_CHANGE_ONLY, KCSAN still reports data
races between reads and watchpointed writes, even if the writes wrote
values already present.  This commit causes KCSAN to unconditionally
skip reporting in this case.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Marco Elver 2020-01-29 16:01:02 +01:00 committed by Ingo Molnar
parent f1bc96210c
commit ad4f8eeca8
1 changed files with 20 additions and 7 deletions
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27
kernel/kcsan/report.c
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@ -130,12 +130,25 @@ static bool rate_limit_report(unsigned long frame1, unsigned long frame2)
* Special rules to skip reporting.
*/
static bool
skip_report(int access_type, bool value_change, unsigned long top_frame)
skip_report(bool value_change, unsigned long top_frame)
{
const bool is_write = (access_type & KCSAN_ACCESS_WRITE) != 0;
if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && is_write &&
!value_change) {
/*
* The first call to skip_report always has value_change==true, since we
* cannot know the value written of an instrumented access. For the 2nd
* call there are 6 cases with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY:
*
* 1. read watchpoint, conflicting write (value_change==true): report;
* 2. read watchpoint, conflicting write (value_change==false): skip;
* 3. write watchpoint, conflicting write (value_change==true): report;
* 4. write watchpoint, conflicting write (value_change==false): skip;
* 5. write watchpoint, conflicting read (value_change==false): skip;
* 6. write watchpoint, conflicting read (value_change==true): impossible;
*
* Cases 1-4 are intuitive and expected; case 5 ensures we do not report
* data races where the write may have rewritten the same value; and
* case 6 is simply impossible.
*/
if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && !value_change) {
/*
* The access is a write, but the data value did not change.
*
@ -228,7 +241,7 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
/*
* Must check report filter rules before starting to print.
*/
if (skip_report(access_type, true, stack_entries[skipnr]))
if (skip_report(true, stack_entries[skipnr]))
return false;
if (type == KCSAN_REPORT_RACE_SIGNAL) {
@ -237,7 +250,7 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
other_frame = other_info.stack_entries[other_skipnr];
/* @value_change is only known for the other thread */
if (skip_report(other_info.access_type, value_change, other_frame))
if (skip_report(value_change, other_frame))
return false;
}