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Marco Elver
bd3cc16d1d
Since commit d353934702 ("serial: 8250: Switch to nbcon console, take
2"), several KCSAN tests fail with CONFIG_KCSAN_VERBOSE=y when using the
8250 console.
With CONFIG_KCSAN_VERBOSE=y, the report prints the racing tasks' IRQ
trace events via print_irqtrace_events(), which marks its output as a
printk emergency section. Within an emergency section, printk() flushes
all pending messages to nbcon consoles synchronously. With a slow
console, the reporting thread can therefore stall for over a second
while holding report_lock, i.e. before the remaining lines of the report
are stored.
The test, however, stops checking for reports after a fixed deadline,
which is easily exceeded by a single slow report:
| [ 5.360278] BUG: KCSAN: data-race in test_kernel_read / test_kernel_write
| [ 5.360303] write to 0xffffffffab95a478 of 8 bytes by task 237 on cpu 7:
| ...
| [ 5.360411] irq event stamp: 23
| [ 6.059836] # test_basic: EXPECTATION FAILED at kernel/kcsan/kcsan_test.c:735
| ...
| [ 6.616416] read to 0xffffffffab95a478 of 8 bytes by task 238 on cpu 9:
Waiting for in-progress reports to complete is insufficient: a slow
report that does not match the expected report still uses up the time
to observe the expected report.
Fix it by pausing the test's time budget while a test-related report is
being printed, bounded by an upper limit to avoid stalling the test
forever. Once a report completes, always check it at least once.
Assisted-by: Antigravity
Signed-off-by: Marco Elver <elver@google.com>