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Add an option for entering KDB on recursive panics

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There are many cases where one would choose avoid entering the debugger
on a normal panic, opting instead to reboot and possibly save a kernel
dump. However, recursive kernel panics are an unusual case that might
warrant attention from a human, so provide a secondary tunable,
debug.debugger_on_recursive_panic, to allow entering the debugger only
when this occurs.

For for simplicity in maintaining existing behaviour, the tunable
defaults to zero.

Reviewed by:	cem, markj
Sponsored by:	NetApp, Inc.
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D27271
This commit is contained in:
Mitchell Horne 2020-11-19 18:03:40 +00:00
parent 24d79e9b63
commit c8a96cdcd9
2 changed files with 18 additions and 1 deletions
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12
share/man/man4/ddb.4
View File

@ -26,7 +26,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd October 17, 2019
.Dd November 19, 2020
.Dt DDB 4
.Os
.Sh NAME
@ -87,6 +87,16 @@ which is the default
unless the
.Dv KDB_UNATTENDED
option is specified.
Similarly, if the
.Va debug.debugger_on_recursive_panic
variable is set to
.Dv 1 ,
then the debugger will be invoked on a recursive kernel panic.
This variable has a default value of
.Dv 0 ,
and has no effect if
.Va debug.debugger_on_panic
is already set non-zero.
.Pp
The current location is called
.Va dot .

7
sys/kern/kern_shutdown.c
View File

@ -127,6 +127,11 @@ SYSCTL_INT(_debug, OID_AUTO, debugger_on_panic,
CTLFLAG_RWTUN | CTLFLAG_SECURE,
&debugger_on_panic, 0, "Run debugger on kernel panic");
static bool debugger_on_recursive_panic = false;
SYSCTL_BOOL(_debug, OID_AUTO, debugger_on_recursive_panic,
CTLFLAG_RWTUN | CTLFLAG_SECURE,
&debugger_on_recursive_panic, 0, "Run debugger on recursive kernel panic");
int debugger_on_trap = 0;
SYSCTL_INT(_debug, OID_AUTO, debugger_on_trap,
CTLFLAG_RWTUN | CTLFLAG_SECURE,
@ -899,6 +904,8 @@ vpanic(const char *fmt, va_list ap)
kdb_backtrace();
if (debugger_on_panic)
kdb_enter(KDB_WHY_PANIC, "panic");
else if (!newpanic && debugger_on_recursive_panic)
kdb_enter(KDB_WHY_PANIC, "re-panic");
#endif
/*thread_lock(td); */
td->td_flags |= TDF_INPANIC;