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Message-ID: <Ya2Zpf8qpgDYiGqM@boqun-archlinux>
Date: Mon, 6 Dec 2021 13:03:33 +0800
From: Boqun Feng <boqun.feng@...il.com>
To: Marco Elver <elver@...gle.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
Alexander Potapenko <glider@...gle.com>,
Borislav Petkov <bp@...en8.de>,
Dmitry Vyukov <dvyukov@...gle.com>,
Ingo Molnar <mingo@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Waiman Long <longman@...hat.com>,
Will Deacon <will@...nel.org>, kasan-dev@...glegroups.com,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, llvm@...ts.linux.dev, x86@...nel.org
Subject: Re: [PATCH v3 08/25] kcsan: Show location access was reordered to
Hi,
On Tue, Nov 30, 2021 at 12:44:16PM +0100, Marco Elver wrote:
> Also show the location the access was reordered to. An example report:
>
> | ==================================================================
> | BUG: KCSAN: data-race in test_kernel_wrong_memorder / test_kernel_wrong_memorder
> |
> | read-write to 0xffffffffc01e61a8 of 8 bytes by task 2311 on cpu 5:
> | test_kernel_wrong_memorder+0x57/0x90
> | access_thread+0x99/0xe0
> | kthread+0x2ba/0x2f0
> | ret_from_fork+0x22/0x30
> |
> | read-write (reordered) to 0xffffffffc01e61a8 of 8 bytes by task 2310 on cpu 7:
> | test_kernel_wrong_memorder+0x57/0x90
> | access_thread+0x99/0xe0
> | kthread+0x2ba/0x2f0
> | ret_from_fork+0x22/0x30
> | |
> | +-> reordered to: test_kernel_wrong_memorder+0x80/0x90
> |
Should this be "reordered from" instead of "reordered to"? For example,
if the following case needs a smp_mb() between write to A and write to
B, I think currently it will report as follow:
foo() {
WRITE_ONCE(A, 1); // let's say A's address is 0xaaaa
bar() {
WRITE_ONCE(B, 1); // Assume B's address is 0xbbbb
// KCSAN find the problem here
}
}
<report>
| write (reordered) to 0xaaaa of ...:
| bar+0x... // address of the write to B
| foo+0x... // address of the callsite to bar()
| ...
| |
| +-> reordered to: foo+0x... // address of the write to A
But since the access reported here is the write to A, so it's a
"reordered from" instead of "reordered to"?
Regards,
Boqun
> | Reported by Kernel Concurrency Sanitizer on:
> | CPU: 7 PID: 2310 Comm: access_thread Not tainted 5.14.0-rc1+ #18
> | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
> | ==================================================================
>
> Signed-off-by: Marco Elver <elver@...gle.com>
> ---
> kernel/kcsan/report.c | 35 +++++++++++++++++++++++------------
> 1 file changed, 23 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
> index 1b0e050bdf6a..67794404042a 100644
> --- a/kernel/kcsan/report.c
> +++ b/kernel/kcsan/report.c
> @@ -308,10 +308,12 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
>
> /*
> * Skips to the first entry that matches the function of @ip, and then replaces
> - * that entry with @ip, returning the entries to skip.
> + * that entry with @ip, returning the entries to skip with @replaced containing
> + * the replaced entry.
> */
> static int
> -replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned long ip)
> +replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned long ip,
> + unsigned long *replaced)
> {
> unsigned long symbolsize, offset;
> unsigned long target_func;
> @@ -330,6 +332,7 @@ replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned lon
> func -= offset;
>
> if (func == target_func) {
> + *replaced = stack_entries[skip];
> stack_entries[skip] = ip;
> return skip;
> }
> @@ -342,9 +345,10 @@ replace_stack_entry(unsigned long stack_entries[], int num_entries, unsigned lon
> }
>
> static int
> -sanitize_stack_entries(unsigned long stack_entries[], int num_entries, unsigned long ip)
> +sanitize_stack_entries(unsigned long stack_entries[], int num_entries, unsigned long ip,
> + unsigned long *replaced)
> {
> - return ip ? replace_stack_entry(stack_entries, num_entries, ip) :
> + return ip ? replace_stack_entry(stack_entries, num_entries, ip, replaced) :
> get_stack_skipnr(stack_entries, num_entries);
> }
>
> @@ -360,6 +364,14 @@ static int sym_strcmp(void *addr1, void *addr2)
> return strncmp(buf1, buf2, sizeof(buf1));
> }
>
> +static void
> +print_stack_trace(unsigned long stack_entries[], int num_entries, unsigned long reordered_to)
> +{
> + stack_trace_print(stack_entries, num_entries, 0);
> + if (reordered_to)
> + pr_err(" |\n +-> reordered to: %pS\n", (void *)reordered_to);
> +}
> +
> static void print_verbose_info(struct task_struct *task)
> {
> if (!task)
> @@ -378,10 +390,12 @@ static void print_report(enum kcsan_value_change value_change,
> struct other_info *other_info,
> u64 old, u64 new, u64 mask)
> {
> + unsigned long reordered_to = 0;
> unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
> int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1);
> - int skipnr = sanitize_stack_entries(stack_entries, num_stack_entries, ai->ip);
> + int skipnr = sanitize_stack_entries(stack_entries, num_stack_entries, ai->ip, &reordered_to);
> unsigned long this_frame = stack_entries[skipnr];
> + unsigned long other_reordered_to = 0;
> unsigned long other_frame = 0;
> int other_skipnr = 0; /* silence uninit warnings */
>
> @@ -394,7 +408,7 @@ static void print_report(enum kcsan_value_change value_change,
> if (other_info) {
> other_skipnr = sanitize_stack_entries(other_info->stack_entries,
> other_info->num_stack_entries,
> - other_info->ai.ip);
> + other_info->ai.ip, &other_reordered_to);
> other_frame = other_info->stack_entries[other_skipnr];
>
> /* @value_change is only known for the other thread */
> @@ -434,10 +448,9 @@ static void print_report(enum kcsan_value_change value_change,
> other_info->ai.cpu_id);
>
> /* Print the other thread's stack trace. */
> - stack_trace_print(other_info->stack_entries + other_skipnr,
> + print_stack_trace(other_info->stack_entries + other_skipnr,
> other_info->num_stack_entries - other_skipnr,
> - 0);
> -
> + other_reordered_to);
> if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> print_verbose_info(other_info->task);
>
> @@ -451,9 +464,7 @@ static void print_report(enum kcsan_value_change value_change,
> get_thread_desc(ai->task_pid), ai->cpu_id);
> }
> /* Print stack trace of this thread. */
> - stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> - 0);
> -
> + print_stack_trace(stack_entries + skipnr, num_stack_entries - skipnr, reordered_to);
> if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> print_verbose_info(current);
>
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>
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