* [PATCH v2] kcsan: Add option for verbose reporting
@ 2020-02-21 22:56 Marco Elver
2020-02-21 23:11 ` Marco Elver
0 siblings, 1 reply; 2+ messages in thread
From: Marco Elver @ 2020-02-21 22:56 UTC (permalink / raw)
To: elver
Cc: paulmck, andreyknvl, glider, dvyukov, kasan-dev, linux-kernel, Qian Cai
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 <elver@google.com>
Suggested-by: Qian Cai <cai@lca.pw>
---
v2:
* Rework obtaining 'current' for the "other thread" -- it now passes
'current' and ensures that we stall until the report was printed, so
that the lockdep information contained in 'current' is accurate. This
was non-trivial but testing so far leads me to conclude this now
reliably prints the held locks for the "other thread" (please test
more!).
---
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 e7387fec66795..065615df88eaa 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 892de5120c1b6..e282f8b5749e9 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 11c791b886f3c..ee8f33d7405fb 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");
@@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
spin_unlock_irqrestore(&report_lock, *flags);
}
+/*
+ * Sets @other_info.task and awaits consumption of @other_info.
+ *
+ * Precondition: report_lock is held.
+ * Postcontiion: 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
@@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
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 081ed2e1bf7b1..0f1447ff8f558 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"
--
2.25.0.265.gbab2e86ba0-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] kcsan: Add option for verbose reporting
2020-02-21 22:56 [PATCH v2] kcsan: Add option for verbose reporting Marco Elver
@ 2020-02-21 23:11 ` Marco Elver
0 siblings, 0 replies; 2+ messages in thread
From: Marco Elver @ 2020-02-21 23:11 UTC (permalink / raw)
To: Marco Elver
Cc: Paul E. McKenney, Andrey Konovalov, Alexander Potapenko,
Dmitry Vyukov, kasan-dev, LKML, Qian Cai
Superseded by v3 due to typos:
http://lkml.kernel.org/r/20200221231027.230147-1-elver@google.com
Thanks,
-- Marco
On Fri, 21 Feb 2020 at 23:57, Marco Elver <elver@google.com> wrote:
>
> 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 <elver@google.com>
> Suggested-by: Qian Cai <cai@lca.pw>
> ---
> v2:
> * Rework obtaining 'current' for the "other thread" -- it now passes
> 'current' and ensures that we stall until the report was printed, so
> that the lockdep information contained in 'current' is accurate. This
> was non-trivial but testing so far leads me to conclude this now
> reliably prints the held locks for the "other thread" (please test
> more!).
> ---
> 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 e7387fec66795..065615df88eaa 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 892de5120c1b6..e282f8b5749e9 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 11c791b886f3c..ee8f33d7405fb 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");
> @@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
> spin_unlock_irqrestore(&report_lock, *flags);
> }
>
> +/*
> + * Sets @other_info.task and awaits consumption of @other_info.
> + *
> + * Precondition: report_lock is held.
> + * Postcontiion: 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
> @@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
> 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 081ed2e1bf7b1..0f1447ff8f558 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"
>
> --
> 2.25.0.265.gbab2e86ba0-goog
>
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