[PATCH 0/5] Update doc and fix some issues about kdump

[PATCH 0/5] Update doc and fix some issues about kdump

[Tiezhu Yang]

Tiezhu Yang (5):
  docs: kdump: update description about sysfs file system support
  docs: kdump: add scp sample to write out the dump file
  kcsan: unset panic_on_warn before calling panic()
  sched: unset panic_on_warn before calling panic()
  kfence: unset panic_on_warn before calling panic()

 Documentation/admin-guide/kdump/kdump.rst | 10 +++++++---
 kernel/kcsan/report.c                     | 10 +++++++++-
 kernel/sched/core.c                       | 11 ++++++++++-
 mm/kfence/report.c                        | 10 +++++++++-
 4 files changed, 35 insertions(+), 6 deletions(-)

-- 
2.1.0

[PATCH 1/5] docs: kdump: update description about sysfs file system support

[Tiezhu Yang]

After commit 6a108a14fa35 ("kconfig: rename CONFIG_EMBEDDED to
CONFIG_EXPERT"), "Configure standard kernel features (for small
systems)" is not exist, we should use "Configure standard kernel
features (expert users)" now.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 Documentation/admin-guide/kdump/kdump.rst | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index cb30ca3d..d187df2 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -146,9 +146,9 @@ System kernel config options
 	CONFIG_SYSFS=y
 
    Note that "sysfs file system support" might not appear in the "Pseudo
-   filesystems" menu if "Configure standard kernel features (for small
-   systems)" is not enabled in "General Setup." In this case, check the
-   .config file itself to ensure that sysfs is turned on, as follows::
+   filesystems" menu if "Configure standard kernel features (expert users)"
+   is not enabled in "General Setup." In this case, check the .config file
+   itself to ensure that sysfs is turned on, as follows::
 
 	grep 'CONFIG_SYSFS' .config
 
-- 
2.1.0

[PATCH 2/5] docs: kdump: add scp sample to write out the dump file

[Tiezhu Yang]

Except cp and makedumpfile, add scp sample to write out the dump file.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 Documentation/admin-guide/kdump/kdump.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
index d187df2..a748e7e 100644
--- a/Documentation/admin-guide/kdump/kdump.rst
+++ b/Documentation/admin-guide/kdump/kdump.rst
@@ -533,6 +533,10 @@ the following command::
 
    cp /proc/vmcore <dump-file>
 
+or use scp to write out the dump file between hosts on a network, e.g::
+
+   scp /proc/vmcore remote_username@remote_ip:<dump-file>
+
 You can also use makedumpfile utility to write out the dump file
 with specified options to filter out unwanted contents, e.g::
 
-- 
2.1.0

[PATCH 3/5] kcsan: unset panic_on_warn before calling panic()

[Tiezhu Yang]

As done in the full WARN() handler, panic_on_warn needs to be cleared
before calling panic() to avoid recursive panics.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 kernel/kcsan/report.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index 6779440..752ab33 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -492,8 +492,16 @@ static void print_report(enum kcsan_value_change value_change,
 	dump_stack_print_info(KERN_DEFAULT);
 	pr_err("==================================================================\n");
 
-	if (panic_on_warn)
+	if (panic_on_warn) {
+		/*
+		 * This thread may hit another WARN() in the panic path.
+		 * Resetting this prevents additional WARN() from panicking the
+		 * system on this thread.  Other threads are blocked by the
+		 * panic_mutex in panic().
+		 */
+		panic_on_warn = 0;
 		panic("panic_on_warn set ...\n");
+	}
 }
 
 static void release_report(unsigned long *flags, struct other_info *other_info)
-- 
2.1.0

[PATCH 4/5] sched: unset panic_on_warn before calling panic()

[Tiezhu Yang]

As done in the full WARN() handler, panic_on_warn needs to be cleared
before calling panic() to avoid recursive panics.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 kernel/sched/core.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 848eaa0..f5b0886 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5524,8 +5524,17 @@ static noinline void __schedule_bug(struct task_struct *prev)
 		pr_err("Preemption disabled at:");
 		print_ip_sym(KERN_ERR, preempt_disable_ip);
 	}
-	if (panic_on_warn)
+
+	if (panic_on_warn) {
+		/*
+		 * This thread may hit another WARN() in the panic path.
+		 * Resetting this prevents additional WARN() from panicking the
+		 * system on this thread.  Other threads are blocked by the
+		 * panic_mutex in panic().
+		 */
+		panic_on_warn = 0;
 		panic("scheduling while atomic\n");
+	}
 
 	dump_stack();
 	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
-- 
2.1.0

[PATCH 5/5] kfence: unset panic_on_warn before calling panic()

[Tiezhu Yang]

As done in the full WARN() handler, panic_on_warn needs to be cleared
before calling panic() to avoid recursive panics.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 mm/kfence/report.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/kfence/report.c b/mm/kfence/report.c
index f93a7b2..9d61a23 100644
--- a/mm/kfence/report.c
+++ b/mm/kfence/report.c
@@ -267,8 +267,16 @@ void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *r
 
 	lockdep_on();
 
-	if (panic_on_warn)
+	if (panic_on_warn) {
+		/*
+		 * This thread may hit another WARN() in the panic path.
+		 * Resetting this prevents additional WARN() from panicking the
+		 * system on this thread.  Other threads are blocked by the
+		 * panic_mutex in panic().
+		 */
+		panic_on_warn = 0;
 		panic("panic_on_warn set ...\n");
+	}
 
 	/* We encountered a memory safety error, taint the kernel! */
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
-- 
2.1.0

Re: [PATCH 4/5] sched: unset panic_on_warn before calling panic()

[Marco Elver]

On Fri, 28 Jan 2022 at 12:42, Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>
> As done in the full WARN() handler, panic_on_warn needs to be cleared
> before calling panic() to avoid recursive panics.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  kernel/sched/core.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 848eaa0..f5b0886 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5524,8 +5524,17 @@ static noinline void __schedule_bug(struct task_struct *prev)
>                 pr_err("Preemption disabled at:");
>                 print_ip_sym(KERN_ERR, preempt_disable_ip);
>         }
> -       if (panic_on_warn)
> +
> +       if (panic_on_warn) {
> +               /*
> +                * This thread may hit another WARN() in the panic path.
> +                * Resetting this prevents additional WARN() from panicking the
> +                * system on this thread.  Other threads are blocked by the
> +                * panic_mutex in panic().
> +                */
> +               panic_on_warn = 0;
>                 panic("scheduling while atomic\n");

I agree this is worth fixing.

But: Why can't the "panic_on_warn = 0" just be moved inside panic(),
instead of copy-pasting this all over the place?

I may be missing something obvious why this hasn't been done before...

Thanks,
-- Marco

Re: [PATCH 4/5] sched: unset panic_on_warn before calling panic()

[Tiezhu Yang]

On 1/28/22 19:52, Marco Elver wrote:
> On Fri, 28 Jan 2022 at 12:42, Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>>
>> As done in the full WARN() handler, panic_on_warn needs to be cleared
>> before calling panic() to avoid recursive panics.
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
>> ---
>>   kernel/sched/core.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 848eaa0..f5b0886 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -5524,8 +5524,17 @@ static noinline void __schedule_bug(struct task_struct *prev)
>>                  pr_err("Preemption disabled at:");
>>                  print_ip_sym(KERN_ERR, preempt_disable_ip);
>>          }
>> -       if (panic_on_warn)
>> +
>> +       if (panic_on_warn) {
>> +               /*
>> +                * This thread may hit another WARN() in the panic path.
>> +                * Resetting this prevents additional WARN() from panicking the
>> +                * system on this thread.  Other threads are blocked by the
>> +                * panic_mutex in panic().
>> +                */
>> +               panic_on_warn = 0;
>>                  panic("scheduling while atomic\n");
> 
> I agree this is worth fixing.
> 
> But: Why can't the "panic_on_warn = 0" just be moved inside panic(),
> instead of copy-pasting this all over the place?

OK, it looks better.

Let me wait for some days, if no more comments, I will send v2
to move "panic_on_warn = 0" inside panic() and remove it from
the other places, like this:

diff --git a/kernel/panic.c b/kernel/panic.c
index 55b50e052ec3..95ba825522dd 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -185,6 +185,16 @@ void panic(const char *fmt, ...)
         int old_cpu, this_cpu;
         bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;

+       if (panic_on_warn) {
+               /*
+                * This thread may hit another WARN() in the panic path.
+                * Resetting this prevents additional WARN() from 
panicking the
+                * system on this thread.  Other threads are blocked by the
+                * panic_mutex in panic().
+                */
+               panic_on_warn = 0;
+       }
+
         /*
          * Disable local interrupts. This will prevent panic_smp_self_stop
          * from deadlocking the first cpu that invokes the panic, since
@@ -576,16 +586,8 @@ void __warn(const char *file, int line, void 
*caller, unsigned taint,
         if (regs)
                 show_regs(regs);

-       if (panic_on_warn) {
-               /*
-                * This thread may hit another WARN() in the panic path.
-                * Resetting this prevents additional WARN() from 
panicking the
-                * system on this thread.  Other threads are blocked by the
-                * panic_mutex in panic().
-                */
-               panic_on_warn = 0;
+       if (panic_on_warn)
                 panic("panic_on_warn set ...\n");
-       }

         if (!regs)
                 dump_stack();
diff --git a/lib/ubsan.c b/lib/ubsan.c
index bdc380ff5d5c..36bd75e33426 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -154,16 +154,8 @@ static void ubsan_epilogue(void)

         current->in_ubsan--;

-       if (panic_on_warn) {
-               /*
-                * This thread may hit another WARN() in the panic path.
-                * Resetting this prevents additional WARN() from 
panicking the
-                * system on this thread.  Other threads are blocked by the
-                * panic_mutex in panic().
-                */
-               panic_on_warn = 0;
+       if (panic_on_warn)
                 panic("panic_on_warn set ...\n");
-       }
  }

  void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs)
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 3ad9624dcc56..f14146563d41 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -117,16 +117,8 @@ static void end_report(unsigned long *flags, 
unsigned long addr)
 
pr_err("==================================================================\n");
         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
         spin_unlock_irqrestore(&report_lock, *flags);
-       if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, 
&kasan_flags)) {
-               /*
-                * This thread may hit another WARN() in the panic path.
-                * Resetting this prevents additional WARN() from 
panicking the
-                * system on this thread.  Other threads are blocked by the
-                * panic_mutex in panic().
-                */
-               panic_on_warn = 0;
+       if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
                 panic("panic_on_warn set ...\n");
-       }
         if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC)
                 panic("kasan.fault=panic set ...\n");
         kasan_enable_current();

Thanks,
Tiezhu

> 
> I may be missing something obvious why this hasn't been done before...
> 
> Thanks,
> -- Marco

Re: [PATCH 1/5] docs: kdump: update description about sysfs file system support

[Baoquan He]

On 01/28/22 at 07:42pm, Tiezhu Yang wrote:
> After commit 6a108a14fa35 ("kconfig: rename CONFIG_EMBEDDED to
> CONFIG_EXPERT"), "Configure standard kernel features (for small
> systems)" is not exist, we should use "Configure standard kernel
> features (expert users)" now.
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  Documentation/admin-guide/kdump/kdump.rst | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index cb30ca3d..d187df2 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -146,9 +146,9 @@ System kernel config options
>  	CONFIG_SYSFS=y
>  
>     Note that "sysfs file system support" might not appear in the "Pseudo
> -   filesystems" menu if "Configure standard kernel features (for small
> -   systems)" is not enabled in "General Setup." In this case, check the
> -   .config file itself to ensure that sysfs is turned on, as follows::
> +   filesystems" menu if "Configure standard kernel features (expert users)"
> +   is not enabled in "General Setup." In this case, check the .config file
> +   itself to ensure that sysfs is turned on, as follows::

Nice clean up, ack.

Acked-by: Baoquan He <bhe@redhat.com>

Re: [PATCH 2/5] docs: kdump: add scp sample to write out the dump file

[Baoquan He]

On 01/28/22 at 07:42pm, Tiezhu Yang wrote:
> Except cp and makedumpfile, add scp sample to write out the dump file.
                                      ~~~~~~? You mean example?

I think we just give example here, but not list all cases. seems
adding scp is nothing bad. Anyway, except of the concern for 'sample':

Acked-by: Baoquan He <bhe@redhat.com>

> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  Documentation/admin-guide/kdump/kdump.rst | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index d187df2..a748e7e 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -533,6 +533,10 @@ the following command::
>  
>     cp /proc/vmcore <dump-file>
>  
> +or use scp to write out the dump file between hosts on a network, e.g::
> +
> +   scp /proc/vmcore remote_username@remote_ip:<dump-file>
> +
>  You can also use makedumpfile utility to write out the dump file
>  with specified options to filter out unwanted contents, e.g::
>  
> -- 
> 2.1.0
>