Re: [PATCH REPOST] lib/ubsan: Don't seralize UBSAN report

[Andre Przywara <andre.przywara@arm.com>]

On Thu, 10 Oct 2019 18:36:16 +0200
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

Hi,

you seem to be me missing the "From:" line here, to keep Julien as the author. If you have this patch in a git repo, you could use:
$ git commit --amend --author "Julien Grall <julien.grall@arm.com>"
so that git keeps the authorship, which should be translated into the proper email form (From: ...) by git send-email.

And what is the reason for the repost anyway?

Cheers,
Andre.

> At the moment, UBSAN report will be serialized using a spin_lock(). On
> RT-systems, spinlocks are turned to rt_spin_lock and may sleep. This will
> result to the following splat if the undefined behavior is in a context
> that can not sleep:
> 
> | BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:968
> | in_atomic(): 1, irqs_disabled(): 128, pid: 3447, name: make
> | 1 lock held by make/3447:
> |  #0: 000000009a966332 (&mm->mmap_sem){++++}, at: do_page_fault+0x140/0x4f8
> | Preemption disabled at:
> | [<ffff000011324a4c>] rt_mutex_futex_unlock+0x4c/0xb0
> | CPU: 3 PID: 3447 Comm: make Tainted: G        W         5.2.14-rt7-01890-ge6e057589653 #911
> | Call trace:
> …
> |  ___might_sleep+0x154/0x210
> |  rt_spin_lock+0x68/0xa0
> |  ubsan_prologue+0x30/0x68
> |  handle_overflow+0x64/0xe0
> |  __ubsan_handle_add_overflow+0x10/0x18
> 
> The spin_lock() will protect against multiple CPUs to output a report
> together, I guess to prevent them to be interleaved. However, they can
> still interleave with other messages (and even splat from __migth_sleep).
> 
> So the lock usefulness seems pretty limited. Rather than trying to
> accomodate RT-system by switching to a raw_spin_lock(), the lock is now
> completely dropped.
> 
> Link: https://lkml.kernel.org/r/20190920100835.14999-1-julien.grall@arm.com
> Reported-by: Andre Przywara <andre.przywara@arm.com>
> Signed-off-by: 
> Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> Repost of
>   https://lkml.kernel.org/r/20190920100835.14999-1-julien.grall@arm.com
> 
>  lib/ubsan.c | 64 +++++++++++++++++++----------------------------------
>  1 file changed, 23 insertions(+), 41 deletions(-)
> 
> diff --git a/lib/ubsan.c b/lib/ubsan.c
> index e7d31735950de..39d5952c42733 100644
> --- a/lib/ubsan.c
> +++ b/lib/ubsan.c
> @@ -140,25 +140,21 @@ static void val_to_string(char *str, size_t size, struct type_descriptor *type,
>  	}
>  }
>  
> -static DEFINE_SPINLOCK(report_lock);
> -
> -static void ubsan_prologue(struct source_location *location,
> -			unsigned long *flags)
> +static void ubsan_prologue(struct source_location *location)
>  {
>  	current->in_ubsan++;
> -	spin_lock_irqsave(&report_lock, *flags);
>  
>  	pr_err("========================================"
>  		"========================================\n");
>  	print_source_location("UBSAN: Undefined behaviour in", location);
>  }
>  
> -static void ubsan_epilogue(unsigned long *flags)
> +static void ubsan_epilogue(void)
>  {
>  	dump_stack();
>  	pr_err("========================================"
>  		"========================================\n");
> -	spin_unlock_irqrestore(&report_lock, *flags);
> +
>  	current->in_ubsan--;
>  }
>  
> @@ -167,14 +163,13 @@ static void handle_overflow(struct overflow_data *data, void *lhs,
>  {
>  
>  	struct type_descriptor *type = data->type;
> -	unsigned long flags;
>  	char lhs_val_str[VALUE_LENGTH];
>  	char rhs_val_str[VALUE_LENGTH];
>  
>  	if (suppress_report(&data->location))
>  		return;
>  
> -	ubsan_prologue(&data->location, &flags);
> +	ubsan_prologue(&data->location);
>  
>  	val_to_string(lhs_val_str, sizeof(lhs_val_str), type, lhs);
>  	val_to_string(rhs_val_str, sizeof(rhs_val_str), type, rhs);
> @@ -186,7 +181,7 @@ static void handle_overflow(struct overflow_data *data, void *lhs,
>  		rhs_val_str,
>  		type->type_name);
>  
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  
>  void __ubsan_handle_add_overflow(struct overflow_data *data,
> @@ -214,20 +209,19 @@ EXPORT_SYMBOL(__ubsan_handle_mul_overflow);
>  void __ubsan_handle_negate_overflow(struct overflow_data *data,
>  				void *old_val)
>  {
> -	unsigned long flags;
>  	char old_val_str[VALUE_LENGTH];
>  
>  	if (suppress_report(&data->location))
>  		return;
>  
> -	ubsan_prologue(&data->location, &flags);
> +	ubsan_prologue(&data->location);
>  
>  	val_to_string(old_val_str, sizeof(old_val_str), data->type, old_val);
>  
>  	pr_err("negation of %s cannot be represented in type %s:\n",
>  		old_val_str, data->type->type_name);
>  
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  EXPORT_SYMBOL(__ubsan_handle_negate_overflow);
>  
> @@ -235,13 +229,12 @@ EXPORT_SYMBOL(__ubsan_handle_negate_overflow);
>  void __ubsan_handle_divrem_overflow(struct overflow_data *data,
>  				void *lhs, void *rhs)
>  {
> -	unsigned long flags;
>  	char rhs_val_str[VALUE_LENGTH];
>  
>  	if (suppress_report(&data->location))
>  		return;
>  
> -	ubsan_prologue(&data->location, &flags);
> +	ubsan_prologue(&data->location);
>  
>  	val_to_string(rhs_val_str, sizeof(rhs_val_str), data->type, rhs);
>  
> @@ -251,58 +244,52 @@ void __ubsan_handle_divrem_overflow(struct overflow_data *data,
>  	else
>  		pr_err("division by zero\n");
>  
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  EXPORT_SYMBOL(__ubsan_handle_divrem_overflow);
>  
>  static void handle_null_ptr_deref(struct type_mismatch_data_common *data)
>  {
> -	unsigned long flags;
> -
>  	if (suppress_report(data->location))
>  		return;
>  
> -	ubsan_prologue(data->location, &flags);
> +	ubsan_prologue(data->location);
>  
>  	pr_err("%s null pointer of type %s\n",
>  		type_check_kinds[data->type_check_kind],
>  		data->type->type_name);
>  
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  
>  static void handle_misaligned_access(struct type_mismatch_data_common *data,
>  				unsigned long ptr)
>  {
> -	unsigned long flags;
> -
>  	if (suppress_report(data->location))
>  		return;
>  
> -	ubsan_prologue(data->location, &flags);
> +	ubsan_prologue(data->location);
>  
>  	pr_err("%s misaligned address %p for type %s\n",
>  		type_check_kinds[data->type_check_kind],
>  		(void *)ptr, data->type->type_name);
>  	pr_err("which requires %ld byte alignment\n", data->alignment);
>  
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  
>  static void handle_object_size_mismatch(struct type_mismatch_data_common *data,
>  					unsigned long ptr)
>  {
> -	unsigned long flags;
> -
>  	if (suppress_report(data->location))
>  		return;
>  
> -	ubsan_prologue(data->location, &flags);
> +	ubsan_prologue(data->location);
>  	pr_err("%s address %p with insufficient space\n",
>  		type_check_kinds[data->type_check_kind],
>  		(void *) ptr);
>  	pr_err("for an object of type %s\n", data->type->type_name);
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  
>  static void ubsan_type_mismatch_common(struct type_mismatch_data_common *data,
> @@ -351,25 +338,23 @@ EXPORT_SYMBOL(__ubsan_handle_type_mismatch_v1);
>  
>  void __ubsan_handle_out_of_bounds(struct out_of_bounds_data *data, void *index)
>  {
> -	unsigned long flags;
>  	char index_str[VALUE_LENGTH];
>  
>  	if (suppress_report(&data->location))
>  		return;
>  
> -	ubsan_prologue(&data->location, &flags);
> +	ubsan_prologue(&data->location);
>  
>  	val_to_string(index_str, sizeof(index_str), data->index_type, index);
>  	pr_err("index %s is out of range for type %s\n", index_str,
>  		data->array_type->type_name);
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  EXPORT_SYMBOL(__ubsan_handle_out_of_bounds);
>  
>  void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
>  					void *lhs, void *rhs)
>  {
> -	unsigned long flags;
>  	struct type_descriptor *rhs_type = data->rhs_type;
>  	struct type_descriptor *lhs_type = data->lhs_type;
>  	char rhs_str[VALUE_LENGTH];
> @@ -378,7 +363,7 @@ void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
>  	if (suppress_report(&data->location))
>  		return;
>  
> -	ubsan_prologue(&data->location, &flags);
> +	ubsan_prologue(&data->location);
>  
>  	val_to_string(rhs_str, sizeof(rhs_str), rhs_type, rhs);
>  	val_to_string(lhs_str, sizeof(lhs_str), lhs_type, lhs);
> @@ -401,18 +386,16 @@ void __ubsan_handle_shift_out_of_bounds(struct shift_out_of_bounds_data *data,
>  			lhs_str, rhs_str,
>  			lhs_type->type_name);
>  
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  EXPORT_SYMBOL(__ubsan_handle_shift_out_of_bounds);
>  
>  
>  void __ubsan_handle_builtin_unreachable(struct unreachable_data *data)
>  {
> -	unsigned long flags;
> -
> -	ubsan_prologue(&data->location, &flags);
> +	ubsan_prologue(&data->location);
>  	pr_err("calling __builtin_unreachable()\n");
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  	panic("can't return from __builtin_unreachable()");
>  }
>  EXPORT_SYMBOL(__ubsan_handle_builtin_unreachable);
> @@ -420,19 +403,18 @@ EXPORT_SYMBOL(__ubsan_handle_builtin_unreachable);
>  void __ubsan_handle_load_invalid_value(struct invalid_value_data *data,
>  				void *val)
>  {
> -	unsigned long flags;
>  	char val_str[VALUE_LENGTH];
>  
>  	if (suppress_report(&data->location))
>  		return;
>  
> -	ubsan_prologue(&data->location, &flags);
> +	ubsan_prologue(&data->location);
>  
>  	val_to_string(val_str, sizeof(val_str), data->type, val);
>  
>  	pr_err("load of value %s is not a valid value for type %s\n",
>  		val_str, data->type->type_name);
>  
> -	ubsan_epilogue(&flags);
> +	ubsan_epilogue();
>  }
>  EXPORT_SYMBOL(__ubsan_handle_load_invalid_value);