linux.git/lib/bug.c, branch v6.18.21

bug: Use RCU instead RCU-sched to protect module_bug_list.

2025-03-10T10:54:46+00:00

The list module_bug_list relies on module_mutex for writer
synchronisation. The list is already RCU style.
The list removal is synchronized with modules' synchronize_rcu() in
free_module().

Use RCU read lock protection instead of RCU-sched.

Cc: Andrew Morton 
Signed-off-by: Sebastian Andrzej Siewior 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20250108090457.512198-29-bigeasy@linutronix.de
Signed-off-by: Petr Pavlu

cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG

2023-01-31T14:01:45+00:00

In order to avoid WARN/BUG from generating nested or even recursive
warnings, force rcu_is_watching() true during
WARN/lockdep_rcu_suspicious().

Notably things like unwinding the stack can trigger rcu_dereference()
warnings, which then triggers more unwinding which then triggers more
warnings etc..

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Link: https://lore.kernel.org/r/20230126151323.408156109@infradead.org

bug: Use normal relative pointers in 'struct bug_entry'

2022-05-19T21:46:10+00:00

With CONFIG_GENERIC_BUG_RELATIVE_POINTERS, the addr/file relative
pointers are calculated weirdly: based on the beginning of the bug_entry
struct address, rather than their respective pointer addresses.

Make the relative pointers less surprising to both humans and tools by
calculating them the normal way.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Mark Rutland 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Sven Schnelle  # s390
Acked-by: Michael Ellerman  (powerpc)
Acked-by: Catalin Marinas 
Tested-by: Mark Rutland  [arm64]
Link: https://lkml.kernel.org/r/f0e05be797a16f4fc2401eeb88c8450dcbe61df6.1652362951.git.jpoimboe@kernel.org

bug: Assign values once in bug_get_file_line()

2021-04-01T08:54:37+00:00

Set bug_get_file_line()'s output parameter values directly rather than
first nullifying them and then conditionally setting new values.

Signed-off-by: Andrew Scull 
Cc: Peter Zijlstra 
Cc: "Steven Rostedt (VMware)" 
Acked-by: Will Deacon 
Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20210318143311.839894-4-ascull@google.com

bug: Factor out a getter for a bug's file line

2021-04-01T08:54:37+00:00

There is some non-trivial config-based logic to get the file name and
line number associated with a bug. Factor this out to a getter that can
be resused.

Signed-off-by: Andrew Scull 
Cc: Peter Zijlstra 
Cc: "Steven Rostedt (VMware)" 
Reviewed-by: Steven Rostedt (VMware) 
Acked-by: Will Deacon 
Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20210318143311.839894-3-ascull@google.com

bug: Remove redundant condition check in report_bug

2021-04-01T08:54:37+00:00

report_bug() will return early if it cannot find a bug corresponding to
the provided address. The subsequent test for the bug will always be
true so remove it.

Fixes: 1b4cfe3c0a30d ("lib/bug.c: exclude non-BUG/WARN exceptions from report_bug()")
Signed-off-by: Andrew Scull 
Cc: Peter Zijlstra 
Cc: "Steven Rostedt (VMware)" 
Reviewed-by: Steven Rostedt (VMware) 
Acked-by: Will Deacon 
Signed-off-by: Marc Zyngier 
Link: https://lore.kernel.org/r/20210318143311.839894-2-ascull@google.com

module: mark module_mutex static

2021-02-08T11:24:26+00:00

Except for two lockdep asserts module_mutex is only used in module.c.
Remove the two asserts given that the functions they are in are not
exported and just called from the module code, and mark module_mutex
static.

Reviewed-by: Miroslav Benes 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Jessica Yu

ftrace,bug: Improve traceoff_on_warn

2020-06-01T12:23:42+00:00

While doing some tracing, I found a huge portion of the per-cpu buffer
was taken by printk/serial output because we're disabling the trace far
too late (after printing the CUT string).

Improve matters for architectures that have GENERIC_BUG + _BUG_FLAGS by
killing the tracer in the exception handler before printing anything
much.

Link: https://lkml.kernel.org/r/20200528145240.GF706495@hirez.programming.kicks-ass.net

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Steven Rostedt (VMware)

bug: move WARN_ON() "cut here" into exception handler

2019-09-26T00:51:41+00:00

The original clean up of "cut here" missed the WARN_ON() case (that does
not have a printk message), which was fixed recently by adding an explicit
printk of "cut here".  This had the downside of adding a printk() to every
WARN_ON() caller, which reduces the utility of using an instruction
exception to streamline the resulting code.  By making this a new BUGFLAG,
all of these can be removed and "cut here" can be handled by the exception
handler.

This was very pronounced on PowerPC, but the effect can be seen on x86 as
well.  The resulting text size of a defconfig build shows some small
savings from this patch:

   text    data     bss     dec     hex filename
19691167        5134320 1646664 26472151        193eed7 vmlinux.before
19676362        5134260 1663048 26473670        193f4c6 vmlinux.after

This change also opens the door for creating something like BUG_MSG(),
where a custom printk() before issuing BUG(), without confusing the "cut
here" line.

Link: http://lkml.kernel.org/r/201908200943.601DD59DCE@keescook
Fixes: 6b15f678fb7d ("include/asm-generic/bug.h: fix "cut here" for WARN_ON for __WARN_TAINT architectures")
Signed-off-by: Kees Cook 
Reported-by: Christophe Leroy 
Cc: Peter Zijlstra 
Cc: Christophe Leroy 
Cc: Drew Davenport 
Cc: Arnd Bergmann 
Cc: "Steven Rostedt (VMware)" 
Cc: Feng Tang 
Cc: Petr Mladek 
Cc: Mauro Carvalho Chehab 
Cc: Borislav Petkov 
Cc: YueHaibing 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

lib/bug.c: exclude non-BUG/WARN exceptions from report_bug()

2018-03-10T00:40:01+00:00

Commit b8347c219649 ("x86/debug: Handle warnings before the notifier
chain, to fix KGDB crash") changed the ordering of fixups, and did not
take into account the case of x86 processing non-WARN() and non-BUG()
exceptions.  This would lead to output of a false BUG line with no other
information.

In the case of a refcount exception, it would be immediately followed by
the refcount WARN(), producing very strange double-"cut here":

  lkdtm: attempting bad refcount_inc() overflow
  ------------[ cut here ]------------
  Kernel BUG at 0000000065f29de5 [verbose debug info unavailable]
  ------------[ cut here ]------------
  refcount_t overflow at lkdtm_REFCOUNT_INC_OVERFLOW+0x6b/0x90 in cat[3065], uid/euid: 0/0
  WARNING: CPU: 0 PID: 3065 at kernel/panic.c:657 refcount_error_report+0x9a/0xa4
  ...

In the prior ordering, exceptions were searched first:

   do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
   ...
                if (fixup_exception(regs, trapnr))
                        return 0;

  -               if (fixup_bug(regs, trapnr))
  -                       return 0;
  -

As a result, fixup_bugs()'s is_valid_bugaddr() didn't take into account
needing to search the exception list first, since that had already
happened.

So, instead of searching the exception list twice (once in
is_valid_bugaddr() and then again in fixup_exception()), just add a
simple sanity check to report_bug() that will immediately bail out if a
BUG() (or WARN()) entry is not found.

Link: http://lkml.kernel.org/r/20180301225934.GA34350@beast
Fixes: b8347c219649 ("x86/debug: Handle warnings before the notifier chain, to fix KGDB crash")
Signed-off-by: Kees Cook 
Cc: Ingo Molnar 
Cc: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Cc: Richard Weinberger 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds