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Merge branch 'kcsan' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into locking/debug

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Pull KCSAN updates from Paul E. McKenney:

 - improve comments
 - introduce CONFIG_KCSAN_STRICT (which RCU uses)
 - optimize use of get_ctx() by kcsan_found_watchpoint()
 - rework atomic.h into permissive.h
 - add the ability to ignore writes that change only one bit of a given data-racy variable.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ingo Molnar
2021-08-18 08:35:23 +02:00
parent 9ae6ab27f4 e04938042d
commit 7f3b457977
6 changed files with 217 additions and 63 deletions
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lib/Kconfig.kcsan
+30 -12
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@@ -40,10 +40,14 @@ menuconfig KCSAN
if KCSAN
# Compiler capabilities that should not fail the test if they are unavailable.
config CC_HAS_TSAN_COMPOUND_READ_BEFORE_WRITE
def_bool (CC_IS_CLANG && $(cc-option,-fsanitize=thread -mllvm -tsan-compound-read-before-write=1)) || \
(CC_IS_GCC && $(cc-option,-fsanitize=thread --param tsan-compound-read-before-write=1))
help
The compiler instruments plain compound read-write operations
differently (++, --, +=, -=, |=, &=, etc.), which allows KCSAN to
distinguish them from other plain accesses. This is currently
supported by Clang 12 or later.
config KCSAN_VERBOSE
bool "Show verbose reports with more information about system state"
@@ -58,9 +62,6 @@ config KCSAN_VERBOSE
generated from any one of them, system stability may suffer due to
deadlocks or recursion. If in doubt, say N.
config KCSAN_DEBUG
bool "Debugging of KCSAN internals"
config KCSAN_SELFTEST
bool "Perform short selftests on boot"
default y
@@ -149,7 +150,8 @@ config KCSAN_SKIP_WATCH_RANDOMIZE
KCSAN_WATCH_SKIP.
config KCSAN_INTERRUPT_WATCHER
bool "Interruptible watchers"
bool "Interruptible watchers" if !KCSAN_STRICT
default KCSAN_STRICT
help
If enabled, a task that set up a watchpoint may be interrupted while
delayed. This option will allow KCSAN to detect races between
@@ -169,13 +171,9 @@ config KCSAN_REPORT_ONCE_IN_MS
reporting to avoid flooding the console with reports. Setting this
to 0 disables rate limiting.
# The main purpose of the below options is to control reported data races (e.g.
# in fuzzer configs), and are not expected to be switched frequently by other
# users. We could turn some of them into boot parameters, but given they should
# not be switched normally, let's keep them here to simplify configuration.
#
# The defaults below are chosen to be very conservative, and may miss certain
# bugs.
# The main purpose of the below options is to control reported data races, and
# are not expected to be switched frequently by non-testers or at runtime.
# The defaults are chosen to be conservative, and can miss certain bugs.
config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
bool "Report races of unknown origin"
@@ -186,9 +184,17 @@ config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
reported if it was only possible to infer a race due to a data value
change while an access is being delayed on a watchpoint.
config KCSAN_STRICT
bool "Strict data-race checking"
help
KCSAN will report data races with the strictest possible rules, which
closely aligns with the rules defined by the Linux-kernel memory
consistency model (LKMM).
config KCSAN_REPORT_VALUE_CHANGE_ONLY
bool "Only report races where watcher observed a data value change"
default y
depends on !KCSAN_STRICT
help
If enabled and a conflicting write is observed via a watchpoint, but
the data value of the memory location was observed to remain
@@ -197,6 +203,7 @@ config KCSAN_REPORT_VALUE_CHANGE_ONLY
config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
bool "Assume that plain aligned writes up to word size are atomic"
default y
depends on !KCSAN_STRICT
help
Assume that plain aligned writes up to word size are atomic by
default, and also not subject to other unsafe compiler optimizations
@@ -209,6 +216,7 @@ config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
config KCSAN_IGNORE_ATOMICS
bool "Do not instrument marked atomic accesses"
depends on !KCSAN_STRICT
help
Never instrument marked atomic accesses. This option can be used for
additional filtering. Conflicting marked atomic reads and plain
@@ -224,4 +232,14 @@ config KCSAN_IGNORE_ATOMICS
due to two conflicting plain writes will be reported (aligned and
unaligned, if CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n).
config KCSAN_PERMISSIVE
bool "Enable all additional permissive rules"
depends on KCSAN_REPORT_VALUE_CHANGE_ONLY
help
Enable additional permissive rules to ignore certain classes of data
races (also see kernel/kcsan/permissive.h). None of the permissive
rules imply that such data races are generally safe, but can be used
to further reduce reported data races due to data-racy patterns
common across the kernel.
endif # KCSAN