* [PATCHv3 0/2] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE @ 2020-03-02 17:51 Dmitry Safonov 2020-03-02 17:51 ` [PATCHv3 1/2] sysctl/sysrq: Remove __sysrq_enabled copy Dmitry Safonov 0 siblings, 1 reply; 4+ messages in thread From: Dmitry Safonov @ 2020-03-02 17:51 UTC (permalink / raw) To: linux-kernel Cc: Dmitry Safonov, Dmitry Safonov, Greg Kroah-Hartman, Iurii Zaikin, Jiri Slaby, Joe Perches, Randy Dunlap, Vasiliy Khoruzhick, linux-serial, Luis Chamberlain, Kees Cook, linux-fsdevel Magic sysrq has proven for Arista usecases to be useful for debugging issues in field, over serial line when the switch is in such bad state that it can't accept network connections anymore. Unfortunately, having sysrq always enabled doesn't work for some embedded boards that tend to generate garbage on serial line (including BREAKs). Since commit 732dbf3a6104 ("serial: do not accept sysrq characters via serial port"), it's possible to keep sysrq enabled, but over serial line. Add a way to enable sysrq on a uart, where currently it can be constantly either on or off (CONFIG_MAGIC_SYSRQ_SERIAL). While doing so, cleanup __sysrq_enabled and serial_core header file. Changes since v2 [2]: - sysrq_get_mask() renamed to sysrq_mask() as there isn't sysrq_put_mask(); acquired kernel-doc (by Greg's review, thanks) - uart_try_toggle_sysrq() now returns true/false instead 1/0 as it's a bool function (nits by Joe Perches, thanks!) - Dropped "sizeof(port->sysrq_seq)*U8_MAX" and used U8_MAX (Randy Dunlap) Changes since v1 [1]: - Fix typo in pr_info() message (noticed by Randy Dunlap, thanks) - Add SYSRQ_TIMEOUT define for timeout after BREAK and separate removing @unused member of uart_port into cleanup patch (by Greg's review, thanks) - Add const qualifier, make uart_try_toggle_sysrq() bool function (Joe Perches, thanks) - Fix !CONFIG_SYSRQ and CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE="" build failures (kudos to kbuild test robot) [1]: https://lkml.kernel.org/r/20200109215444.95995-1-dima@arista.com [2]: https://lkml.kernel.org/r/20200114171912.261787-1-dima@arista.com Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Iurii Zaikin <yzaikin@google.com> Cc: Jiri Slaby <jslaby@suse.com> Cc: Joe Perches <joe@perches.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Vasiliy Khoruzhick <vasilykh@arista.com> Cc: linux-serial@vger.kernel.org Thanks, Dmitry Dmitry Safonov (2): sysctl/sysrq: Remove __sysrq_enabled copy serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE drivers/tty/serial/serial_core.c | 75 +++++++++++++++++++++++++++++--- drivers/tty/sysrq.c | 12 +++++ include/linux/serial_core.h | 1 + include/linux/sysrq.h | 7 +++ kernel/sysctl.c | 41 +++++++++-------- lib/Kconfig.debug | 8 ++++ 6 files changed, 118 insertions(+), 26 deletions(-) -- 2.25.0 ^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCHv3 1/2] sysctl/sysrq: Remove __sysrq_enabled copy 2020-03-02 17:51 [PATCHv3 0/2] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE Dmitry Safonov @ 2020-03-02 17:51 ` Dmitry Safonov 2020-04-01 12:22 ` Michael Ellerman 0 siblings, 1 reply; 4+ messages in thread From: Dmitry Safonov @ 2020-03-02 17:51 UTC (permalink / raw) To: linux-kernel Cc: Dmitry Safonov, Dmitry Safonov, Greg Kroah-Hartman, Iurii Zaikin, Jiri Slaby, Joe Perches, Randy Dunlap, Vasiliy Khoruzhick, linux-serial, Luis Chamberlain, Kees Cook, linux-fsdevel Many embedded boards have a disconnected TTL level serial which can generate some garbage that can lead to spurious false sysrq detects. Currently, sysrq can be either completely disabled for serial console or always disabled (with CONFIG_MAGIC_SYSRQ_SERIAL), since commit 732dbf3a6104 ("serial: do not accept sysrq characters via serial port") At Arista, we have such boards that can generate BREAK and random garbage. While disabling sysrq for serial console would solve the problem with spurious false sysrq triggers, it's also desirable to have a way to enable sysrq back. Having the way to enable sysrq was beneficial to debug lockups with a manual investigation in field and on the other side preventing false sysrq detections. As a preparation to add sysrq_toggle_support() call into uart, remove a private copy of sysrq_enabled from sysctl - it should reflect the actual status of sysrq. Furthermore, the private copy isn't correct already in case sysrq_always_enabled is true. So, remove __sysrq_enabled and use a getter-helper sysrq_mask() to check sysrq_key_op enabled status. Cc: Iurii Zaikin <yzaikin@google.com> Cc: Jiri Slaby <jslaby@suse.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Dmitry Safonov <dima@arista.com> --- drivers/tty/sysrq.c | 12 ++++++++++++ include/linux/sysrq.h | 7 +++++++ kernel/sysctl.c | 41 ++++++++++++++++++++++------------------- 3 files changed, 41 insertions(+), 19 deletions(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index f724962a5906..5e0d0813da55 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -63,6 +63,18 @@ static bool sysrq_on(void) return sysrq_enabled || sysrq_always_enabled; } +/** + * sysrq_mask - Getter for sysrq_enabled mask. + * + * Return: 1 if sysrq is always enabled, enabled sysrq_key_op mask otherwise. + */ +int sysrq_mask(void) +{ + if (sysrq_always_enabled) + return 1; + return sysrq_enabled; +} + /* * A value of 1 means 'all', other nonzero values are an op mask: */ diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h index 8c71874e8485..8e159e16850f 100644 --- a/include/linux/sysrq.h +++ b/include/linux/sysrq.h @@ -50,6 +50,7 @@ int unregister_sysrq_key(int key, struct sysrq_key_op *op); struct sysrq_key_op *__sysrq_get_key_op(int key); int sysrq_toggle_support(int enable_mask); +int sysrq_mask(void); #else @@ -71,6 +72,12 @@ static inline int unregister_sysrq_key(int key, struct sysrq_key_op *op) return -EINVAL; } +static inline int sysrq_mask(void) +{ + /* Magic SysRq disabled mask */ + return 0; +} + #endif #endif /* _LINUX_SYSRQ_H */ diff --git a/kernel/sysctl.c b/kernel/sysctl.c index ad5b88a53c5a..94638f695e60 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -229,25 +229,8 @@ static int proc_dopipe_max_size(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos); #ifdef CONFIG_MAGIC_SYSRQ -/* Note: sysrq code uses its own private copy */ -static int __sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE; - static int sysrq_sysctl_handler(struct ctl_table *table, int write, - void __user *buffer, size_t *lenp, - loff_t *ppos) -{ - int error; - - error = proc_dointvec(table, write, buffer, lenp, ppos); - if (error) - return error; - - if (write) - sysrq_toggle_support(__sysrq_enabled); - - return 0; -} - + void __user *buffer, size_t *lenp, loff_t *ppos); #endif static struct ctl_table kern_table[]; @@ -747,7 +730,7 @@ static struct ctl_table kern_table[] = { #ifdef CONFIG_MAGIC_SYSRQ { .procname = "sysrq", - .data = &__sysrq_enabled, + .data = NULL, .maxlen = sizeof (int), .mode = 0644, .proc_handler = sysrq_sysctl_handler, @@ -2835,6 +2818,26 @@ static int proc_dostring_coredump(struct ctl_table *table, int write, } #endif +#ifdef CONFIG_MAGIC_SYSRQ +static int sysrq_sysctl_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + int tmp, ret; + + tmp = sysrq_mask(); + + ret = __do_proc_dointvec(&tmp, table, write, buffer, + lenp, ppos, NULL, NULL); + if (ret || !write) + return ret; + + if (write) + sysrq_toggle_support(tmp); + + return 0; +} +#endif + static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos, -- 2.25.0 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCHv3 1/2] sysctl/sysrq: Remove __sysrq_enabled copy 2020-03-02 17:51 ` [PATCHv3 1/2] sysctl/sysrq: Remove __sysrq_enabled copy Dmitry Safonov @ 2020-04-01 12:22 ` Michael Ellerman 2020-04-01 14:41 ` Dmitry Safonov 0 siblings, 1 reply; 4+ messages in thread From: Michael Ellerman @ 2020-04-01 12:22 UTC (permalink / raw) To: Dmitry Safonov, linux-kernel Cc: Dmitry Safonov, Dmitry Safonov, Greg Kroah-Hartman, Iurii Zaikin, Jiri Slaby, Joe Perches, Randy Dunlap, Vasiliy Khoruzhick, linux-serial, Luis Chamberlain, Kees Cook, linux-fsdevel Dmitry Safonov <dima@arista.com> writes: > Many embedded boards have a disconnected TTL level serial which can > generate some garbage that can lead to spurious false sysrq detects. > > Currently, sysrq can be either completely disabled for serial console > or always disabled (with CONFIG_MAGIC_SYSRQ_SERIAL), since > commit 732dbf3a6104 ("serial: do not accept sysrq characters via serial port") > > At Arista, we have such boards that can generate BREAK and random > garbage. While disabling sysrq for serial console would solve > the problem with spurious false sysrq triggers, it's also desirable > to have a way to enable sysrq back. > > Having the way to enable sysrq was beneficial to debug lockups with > a manual investigation in field and on the other side preventing false > sysrq detections. > > As a preparation to add sysrq_toggle_support() call into uart, > remove a private copy of sysrq_enabled from sysctl - it should reflect > the actual status of sysrq. > > Furthermore, the private copy isn't correct already in case > sysrq_always_enabled is true. So, remove __sysrq_enabled and use a > getter-helper sysrq_mask() to check sysrq_key_op enabled status. > > Cc: Iurii Zaikin <yzaikin@google.com> > Cc: Jiri Slaby <jslaby@suse.com> > Cc: Luis Chamberlain <mcgrof@kernel.org> > Cc: Kees Cook <keescook@chromium.org> > Cc: linux-fsdevel@vger.kernel.org > Signed-off-by: Dmitry Safonov <dima@arista.com> > --- > drivers/tty/sysrq.c | 12 ++++++++++++ > include/linux/sysrq.h | 7 +++++++ > kernel/sysctl.c | 41 ++++++++++++++++++++++------------------- > 3 files changed, 41 insertions(+), 19 deletions(-) > > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c > index f724962a5906..5e0d0813da55 100644 > --- a/drivers/tty/sysrq.c > +++ b/drivers/tty/sysrq.c > @@ -63,6 +63,18 @@ static bool sysrq_on(void) > return sysrq_enabled || sysrq_always_enabled; > } > > +/** > + * sysrq_mask - Getter for sysrq_enabled mask. > + * > + * Return: 1 if sysrq is always enabled, enabled sysrq_key_op mask otherwise. > + */ > +int sysrq_mask(void) > +{ > + if (sysrq_always_enabled) > + return 1; > + return sysrq_enabled; > +} This seems to have broken several configs, when serial_core is modular, with: ERROR: modpost: "sysrq_mask" [drivers/tty/serial/serial_core.ko] undefined! See: http://kisskb.ellerman.id.au/kisskb/buildresult/14169386/ It's also being reported by the kernelci bot: https://lore.kernel.org/linux-next/5e677bd0.1c69fb81.c43fe.7f7d@mx.google.com/ cheers ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCHv3 1/2] sysctl/sysrq: Remove __sysrq_enabled copy 2020-04-01 12:22 ` Michael Ellerman @ 2020-04-01 14:41 ` Dmitry Safonov 0 siblings, 0 replies; 4+ messages in thread From: Dmitry Safonov @ 2020-04-01 14:41 UTC (permalink / raw) To: Michael Ellerman, linux-kernel Cc: Dmitry Safonov, Greg Kroah-Hartman, Iurii Zaikin, Jiri Slaby, Joe Perches, Randy Dunlap, Vasiliy Khoruzhick, linux-serial, Luis Chamberlain, Kees Cook, linux-fsdevel Hi Michael, On 4/1/20 1:22 PM, Michael Ellerman wrote: [..] >> >> +/** >> + * sysrq_mask - Getter for sysrq_enabled mask. >> + * >> + * Return: 1 if sysrq is always enabled, enabled sysrq_key_op mask otherwise. >> + */ >> +int sysrq_mask(void) >> +{ >> + if (sysrq_always_enabled) >> + return 1; >> + return sysrq_enabled; >> +} > > This seems to have broken several configs, when serial_core is modular, with: > > ERROR: modpost: "sysrq_mask" [drivers/tty/serial/serial_core.ko] undefined! > > See: > > http://kisskb.ellerman.id.au/kisskb/buildresult/14169386/ > > It's also being reported by the kernelci bot: > > https://lore.kernel.org/linux-next/5e677bd0.1c69fb81.c43fe.7f7d@mx.google.com/ Thanks for reporting this, I've reproduced it and sent a fix: https://lkml.kernel.org/r/20200401143904.423450-1-dima@arista.com Thanks, Dmitry ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-04-01 14:41 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2020-03-02 17:51 [PATCHv3 0/2] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE Dmitry Safonov 2020-03-02 17:51 ` [PATCHv3 1/2] sysctl/sysrq: Remove __sysrq_enabled copy Dmitry Safonov 2020-04-01 12:22 ` Michael Ellerman 2020-04-01 14:41 ` Dmitry Safonov
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