| Message ID | cc3b9b1aae60a236c6aed1dc7b0ffa2c7cd1f183.1710220326.git.sreenath.vijayan@sony.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add support to replay kernel log on consoles via sysrq | expand |
On Wed, Mar 13, 2024 at 03:52:52PM +0530, Sreenath Vijayan wrote: > When terminal is unresponsive, one cannot use dmesg to view > the printk ring buffer messages. Also, syslog services may be > disabled, especially on embedded systems, to check the messages > after a reboot. In this scenario, replay the messages in printk > ring buffer on consoles via sysrq by pressing sysrq+R. > > The console loglevel will determine which all kernel log messages > are displayed. The messages will be displayed only when > console_trylock() succeeds. Users could repeat the sysrq key when > it fails. If the owner of console subsystem lock is stuck, > repeating the key won't work. > > Suggested-by: Petr Mladek <pmladek@suse.com> > Signed-off-by: Shimoyashiki Taichi <taichi.shimoyashiki@sony.com> > Reviewed-by: John Ogness <john.ogness@linutronix.de> > Signed-off-by: Sreenath Vijayan <sreenath.vijayan@sony.com> > --- > Documentation/admin-guide/sysrq.rst | 9 +++++++++ > drivers/tty/sysrq.c | 13 ++++++++++++- > 2 files changed, 21 insertions(+), 1 deletion(-) > > diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst > index 2f2e5bd440f9..a85b3384d1e7 100644 > --- a/Documentation/admin-guide/sysrq.rst > +++ b/Documentation/admin-guide/sysrq.rst > @@ -161,6 +161,8 @@ Command Function > will be printed to your console. (``0``, for example would make > it so that only emergency messages like PANICs or OOPSes would > make it to your console.) > + > +``R`` Replay the kernel log messages on consoles. > =========== =================================================================== > > Okay, so what can I use them for? > @@ -211,6 +213,13 @@ processes. > "just thaw ``it(j)``" is useful if your system becomes unresponsive due to a > frozen (probably root) filesystem via the FIFREEZE ioctl. > > +``Replay logs(R)`` is useful to view the kernel log messages when system is hung > +or you are not able to use dmesg command to view the messages in printk buffer. > +User may have to press the key combination multiple times if console system is > +busy. If it is completely locked up, then messages won't be printed. Output > +messages depend on current console loglevel, which can be modified using > +sysrq[0-9] (see above). > + > Sometimes SysRq seems to get 'stuck' after using it, what can I do? > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c > index 02217e3c916b..e5974b8239c9 100644 > --- a/drivers/tty/sysrq.c > +++ b/drivers/tty/sysrq.c > @@ -450,6 +450,17 @@ static const struct sysrq_key_op sysrq_unrt_op = { > .enable_mask = SYSRQ_ENABLE_RTNICE, > }; > > +static void sysrq_handle_replay_logs(u8 key) > +{ > + console_replay_all(); > +} > +static struct sysrq_key_op sysrq_replay_logs_op = { > + .handler = sysrq_handle_replay_logs, > + .help_msg = "replay-kernel-logs(R)", > + .action_msg = "Replay kernel logs on consoles", > + .enable_mask = SYSRQ_ENABLE_DUMP, > +}; > + > /* Key Operations table and lock */ > static DEFINE_SPINLOCK(sysrq_key_table_lock); > > @@ -519,7 +530,7 @@ static const struct sysrq_key_op *sysrq_key_table[62] = { > NULL, /* O */ > NULL, /* P */ > NULL, /* Q */ > - NULL, /* R */ > + &sysrq_replay_logs_op, /* R */ > NULL, /* S */ > NULL, /* T */ > NULL, /* U */ > -- > 2.25.1 > Hi, Kindly let me know if there are any review comments for the above changes. Regards, Sreenath
diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst index 2f2e5bd440f9..a85b3384d1e7 100644 --- a/Documentation/admin-guide/sysrq.rst +++ b/Documentation/admin-guide/sysrq.rst @@ -161,6 +161,8 @@ Command Function will be printed to your console. (``0``, for example would make it so that only emergency messages like PANICs or OOPSes would make it to your console.) + +``R`` Replay the kernel log messages on consoles. =========== =================================================================== Okay, so what can I use them for? @@ -211,6 +213,13 @@ processes. "just thaw ``it(j)``" is useful if your system becomes unresponsive due to a frozen (probably root) filesystem via the FIFREEZE ioctl. +``Replay logs(R)`` is useful to view the kernel log messages when system is hung +or you are not able to use dmesg command to view the messages in printk buffer. +User may have to press the key combination multiple times if console system is +busy. If it is completely locked up, then messages won't be printed. Output +messages depend on current console loglevel, which can be modified using +sysrq[0-9] (see above). + Sometimes SysRq seems to get 'stuck' after using it, what can I do? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 02217e3c916b..e5974b8239c9 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -450,6 +450,17 @@ static const struct sysrq_key_op sysrq_unrt_op = { .enable_mask = SYSRQ_ENABLE_RTNICE, }; +static void sysrq_handle_replay_logs(u8 key) +{ + console_replay_all(); +} +static struct sysrq_key_op sysrq_replay_logs_op = { + .handler = sysrq_handle_replay_logs, + .help_msg = "replay-kernel-logs(R)", + .action_msg = "Replay kernel logs on consoles", + .enable_mask = SYSRQ_ENABLE_DUMP, +}; + /* Key Operations table and lock */ static DEFINE_SPINLOCK(sysrq_key_table_lock); @@ -519,7 +530,7 @@ static const struct sysrq_key_op *sysrq_key_table[62] = { NULL, /* O */ NULL, /* P */ NULL, /* Q */ - NULL, /* R */ + &sysrq_replay_logs_op, /* R */ NULL, /* S */ NULL, /* T */ NULL, /* U */