Messages in this thread | | | Date | Thu, 23 Jul 2009 06:46:21 -0400 | From | Neil Horman <> | Subject | Re: [PATCH] sysrq, kdump: Make sysrq-c consistent |
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On Thu, Jul 23, 2009 at 02:12:10PM +0900, Hidetoshi Seto wrote: > [ based on 2.6.31-rc4 ] > > Recent commit d6580a9f15238b87e618310c862231ae3f352d2d changed the > behavior of sysrq-c to unconditional dereference of NULL pointer. > So in cases with CONFIG_KEXEC, where crash_kexec() was directly called > from sysrq-c before, now it can be said that a step of "real oops" was > inserted before starting kdump. > > However, in contrast to oops via SysRq-c from keyboard which results > in panic due to in_interrupt(), oops via "echo c > /proc/sysrq-trigger" > will not become panic unless panic_on_oops=1. It means that even if > dump is properly configured to be taken on panic, the sysrq-c from proc > interface might not start crashdump while the sysrq-c from keyboard can > start crashdump. This confuses traditional users of kdump, i.e. people > who expect sysrq-c to do common behavior in both of the keyboard and > proc interface. > > This patch brings the keyboard and proc interface behavior of sysrq-c > in line, by forcing panic_on_oops=1 before oops in sysrq-c handler. > > And some updates in documentation are included, to clarify that there > is no longer dependency with CONFIG_KEXEC, and that now the system can > just crash by sysrq-c if no dump mechanism is configured. > Acked-by: Neil Horman <nhorman@tuxdriver.com>
Thanks! Neil
> Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> > Cc: Lai Jiangshan <laijs@cn.fujitsu.com> > Cc: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp> > Cc: Neil Horman <nhorman@tuxdriver.com> > Cc: Vivek Goyal <vgoyal@redhat.com> > Cc: Brayan Arraes <brayan@yack.com.br> > Cc: Eric W. Biederman <ebiederm@xmission.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > --- > Documentation/sysrq.txt | 7 ++++--- > drivers/char/sysrq.c | 8 +++++--- > 2 files changed, 9 insertions(+), 6 deletions(-) > > diff --git a/Documentation/sysrq.txt b/Documentation/sysrq.txt > index cf42b82..d56a017 100644 > --- a/Documentation/sysrq.txt > +++ b/Documentation/sysrq.txt > @@ -66,7 +66,8 @@ On all - write a character to /proc/sysrq-trigger. e.g.: > 'b' - Will immediately reboot the system without syncing or unmounting > your disks. > > -'c' - Will perform a kexec reboot in order to take a crashdump. > +'c' - Will perform a system crash by a NULL pointer dereference. > + A crashdump will be taken if configured. > > 'd' - Shows all locks that are held. > > @@ -141,8 +142,8 @@ useful when you want to exit a program that will not let you switch consoles. > re'B'oot is good when you're unable to shut down. But you should also 'S'ync > and 'U'mount first. > > -'C'rashdump can be used to manually trigger a crashdump when the system is hung. > -The kernel needs to have been built with CONFIG_KEXEC enabled. > +'C'rash can be used to manually trigger a crashdump when the system is hung. > +Note that this just triggers a crash if there is no dump mechanism available. > > 'S'ync is great when your system is locked up, it allows you to sync your > disks and will certainly lessen the chance of data loss and fscking. Note > diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c > index 0db3585..5d7a02f 100644 > --- a/drivers/char/sysrq.c > +++ b/drivers/char/sysrq.c > @@ -35,7 +35,6 @@ > #include <linux/spinlock.h> > #include <linux/vt_kern.h> > #include <linux/workqueue.h> > -#include <linux/kexec.h> > #include <linux/hrtimer.h> > #include <linux/oom.h> > > @@ -124,9 +123,12 @@ static struct sysrq_key_op sysrq_unraw_op = { > static void sysrq_handle_crash(int key, struct tty_struct *tty) > { > char *killer = NULL; > + > + panic_on_oops = 1; /* force panic */ > + wmb(); > *killer = 1; > } > -static struct sysrq_key_op sysrq_crashdump_op = { > +static struct sysrq_key_op sysrq_crash_op = { > .handler = sysrq_handle_crash, > .help_msg = "Crash", > .action_msg = "Trigger a crash", > @@ -401,7 +403,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = { > */ > NULL, /* a */ > &sysrq_reboot_op, /* b */ > - &sysrq_crashdump_op, /* c & ibm_emac driver debug */ > + &sysrq_crash_op, /* c & ibm_emac driver debug */ > &sysrq_showlocks_op, /* d */ > &sysrq_term_op, /* e */ > &sysrq_moom_op, /* f */ > -- > 1.6.0 > >
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