The following commit has been merged into the locking/kcsan branch of tip:
Commit-ID: 2402d0eae589a31ee7b1774cb220d84d0f5605b4
Gitweb:
https://git.kernel.org/tip/2402d0eae589a31ee7b1774cb220d84d0f5605b4
Author: Marco Elver <el...@google.com>
AuthorDate: Sat, 22 Feb 2020 00:10:27 +01:00
Committer: Paul E. McKenney <paul...@kernel.org>
CommitterDate: Wed, 25 Mar 2020 09:56:00 -07:00
kcsan: Add option for verbose reporting
Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports.
Currently information about the reporting task's held locks and IRQ
trace events are shown, if they are enabled.
Signed-off-by: Marco Elver <el...@google.com>
Suggested-by: Qian Cai <c...@lca.pw>
Signed-off-by: Paul E. McKenney <paul...@kernel.org>
---
kernel/kcsan/core.c | 4 +-
kernel/kcsan/kcsan.h | 3 +-
kernel/kcsan/report.c | 103 ++++++++++++++++++++++++++++++++++++++++-
lib/Kconfig.kcsan | 13 +++++-
4 files changed, 120 insertions(+), 3 deletions(-)
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index e7387fe..065615d 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -18,8 +18,8 @@
#include "kcsan.h"
static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
-static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
-static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
+unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
+unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
static bool kcsan_interrupt_watcher =
IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 892de51..e282f8b 100644
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -13,6 +13,9 @@
/* The number of adjacent watchpoints to check. */
#define KCSAN_CHECK_ADJACENT 1
+extern unsigned int kcsan_udelay_task;
+extern unsigned int kcsan_udelay_interrupt;
+
/*
* Globally enable and disable KCSAN.
*/
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index 11c791b..18f9d3b 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -1,5 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
+#include <linux/debug_locks.h>
+#include <linux/delay.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/lockdep.h>
@@ -31,7 +33,26 @@ static struct {
int cpu_id;
unsigned long stack_entries[NUM_STACK_ENTRIES];
int num_stack_entries;
-} other_info = { .ptr = NULL };
+
+ /*
+ * Optionally pass @current. Typically we do not need to pass @current
+ * via @other_info since just @task_pid is sufficient. Passing @current
+ * has additional overhead.
+ *
+ * To safely pass @current, we must either use get_task_struct/
+ * put_task_struct, or stall the thread that populated @other_info.
+ *
+ * We cannot rely on get_task_struct/put_task_struct in case
+ * release_report() races with a task being released, and would have to
+ * free it in release_report(). This may result in deadlock if we want
+ * to use KCSAN on the allocators.
+ *
+ * Since we also want to reliably print held locks for
+ * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
+ * that populated @other_info until it has been consumed.
+ */
+ struct task_struct *task;
+} other_info;
/*
* Information about reported races; used to rate limit reporting.
@@ -245,6 +266,16 @@ static int sym_strcmp(void *addr1, void *addr2)
return strncmp(buf1, buf2, sizeof(buf1));
}
+static void print_verbose_info(struct task_struct *task)
+{
+ if (!task)
+ return;
+
+ pr_err("\n");
+ debug_show_held_locks(task);
+ print_irqtrace_events(task);
+}
+
/*
* Returns true if a report was generated, false otherwise.
*/
@@ -319,6 +350,9 @@ static bool print_report(const volatile void *ptr, size_t
size, int access_type,
other_info.num_stack_entries - other_skipnr,
0);
+ if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
+ print_verbose_info(other_info.task);
+
pr_err("\n");
pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
get_access_type(access_type), ptr, size,
@@ -340,6 +374,9 @@ static bool print_report(const volatile void *ptr, size_t
size, int access_type,
stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
0);
+ if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
+ print_verbose_info(current);
+
/* Print report footer. */
pr_err("\n");
pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
@@ -358,6 +395,67 @@ static void release_report(unsigned long *flags, enum
kcsan_report_type type)
}
/*
+ * Sets @other_info.task and awaits consumption of @other_info.
+ *
+ * Precondition: report_lock is held.
+ * Postcondition: report_lock is held.
+ */
+static void
+set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)
+{
+ /*
+ * We may be instrumenting a code-path where current->state is already
+ * something other than TASK_RUNNING.
+ */
+ const bool is_running = current->state == TASK_RUNNING;
+ /*
+ * To avoid deadlock in case we are in an interrupt here and this is a
+ * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
+ * timeout to ensure this works in all contexts.
+ *
+ * Await approximately the worst case delay of the reporting thread (if
+ * we are not interrupted).
+ */
+ int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
+
+ other_info.task = current;
+ do {
+ if (is_running) {
+ /*
+ * Let lockdep know the real task is sleeping, to print
+ * the held locks (recall we turned lockdep off, so
+ * locking/unlocking @report_lock won't be recorded).
+ */
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ }
+ spin_unlock_irqrestore(&report_lock, *flags);
+ /*
+ * We cannot call schedule() since we also cannot reliably
+ * determine if sleeping here is permitted -- see in_atomic().
+ */
+
+ udelay(1);
+ spin_lock_irqsave(&report_lock, *flags);
+ if (timeout-- < 0) {
+ /*
+ * Abort. Reset other_info.task to NULL, since it
+ * appears the other thread is still going to consume
+ * it. It will result in no verbose info printed for
+ * this task.
+ */
+ other_info.task = NULL;
+ break;
+ }
+ /*
+ * If @ptr nor @current matches, then our information has been
+ * consumed and we may continue. If not, retry.
+ */
+ } while (other_info.ptr == ptr && other_info.task == current);
+ if (is_running)
+ set_current_state(TASK_RUNNING);
+}
+
+/*
* Depending on the report type either sets other_info and returns false, or
* acquires the matching other_info and returns true. If other_info is not
* required for the report type, simply acquires report_lock and returns true.
@@ -388,6 +486,9 @@ retry:
other_info.cpu_id = cpu_id;
other_info.num_stack_entries =
stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
+ if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
+ set_other_info_task_blocking(flags, ptr);
+
spin_unlock_irqrestore(&report_lock, *flags);
/*
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 081ed2e..0f1447f 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -20,6 +20,19 @@ menuconfig KCSAN
if KCSAN
+config KCSAN_VERBOSE
+ bool "Show verbose reports with more information about system state"
+ depends on PROVE_LOCKING
+ help
+ If enabled, reports show more information about the system state that
+ may help better analyze and debug races. This includes held locks and
+ IRQ trace events.
+
+ While this option should generally be benign, we call into more
+ external functions on report generation; if a race report is
+ 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"
