The patch titled sysrq, kdump: make sysrq-c consistent has been added to the -mm tree. Its filename is sysrq-kdump-make-sysrq-c-consistent.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: sysrq, kdump: make sysrq-c consistent From: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx> commit d6580a9f15238b87e618310c862231ae3f352d2d ("kexec: sysrq: simplify sysrq-c handler") 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. Signed-off-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx> Cc: Lai Jiangshan <laijs@xxxxxxxxxxxxxx> Cc: Ken'ichi Ohmichi <oomichi@xxxxxxxxxxxxxxxxx> Acked-by: Neil Horman <nhorman@xxxxxxxxxxxxx> Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx> Cc: Brayan Arraes <brayan@xxxxxxxxxxx> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/sysrq.txt | 7 ++++--- drivers/char/sysrq.c | 8 +++++--- 2 files changed, 9 insertions(+), 6 deletions(-) diff -puN Documentation/sysrq.txt~sysrq-kdump-make-sysrq-c-consistent Documentation/sysrq.txt --- a/Documentation/sysrq.txt~sysrq-kdump-make-sysrq-c-consistent +++ a/Documentation/sysrq.txt @@ -66,7 +66,8 @@ On all - write a character to /proc/sys '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 t 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 -puN drivers/char/sysrq.c~sysrq-kdump-make-sysrq-c-consistent drivers/char/sysrq.c --- a/drivers/char/sysrq.c~sysrq-kdump-make-sysrq-c-consistent +++ a/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_o 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_ta */ 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 */ _ Patches currently in -mm which might be from seto.hidetoshi@xxxxxxxxxxxxxx are kexec-fix-omitting-offset-in-extended-crashkernel-syntax.patch sysrq-kdump-make-sysrq-c-consistent.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html