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Date: Wed, 12 Aug 2020 13:45:44 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
linux-input@...r.kernel.org, kernel@...labora.com
Subject: Re: [PATCH 2/2] tty/sysrq: Add configurable handler to execute a
compound action
On 04. 08. 20, 18:24, Andrzej Pietrasiewicz wrote:
> Userland might want to execute e.g. 'w' (show blocked tasks), followed
> by 's' (sync), followed by 1000 ms delay and then followed by 'c' (crash)
> upon a single magic SysRq. Or one might want to execute the famous "Raising
> Elephants Is So Utterly Boring" action. This patch adds a configurable
> handler, triggered with 'C', for this exact purpose. The user specifies the
> composition of the compound action using syntax similar to getopt, where
> each letter corresponds to an individual action and a colon followed by a
> number corresponds to a delay of that many milliseconds, e.g.:
>
> ws:1000c
>
> or
>
> r:100eis:1000ub
I think I miss what's that good for, given I can do it one-by-one
without setting such strings anywhere (I usually want to do different
things on different kinds of crashes)?
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
> ---
> Documentation/admin-guide/sysrq.rst | 9 ++++
> drivers/tty/sysrq.c | 81 ++++++++++++++++++++++++++++-
> include/linux/sysrq.h | 1 +
> 3 files changed, 90 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
> index 67dfa4c29093..80bdd8bf9636 100644
> --- a/Documentation/admin-guide/sysrq.rst
> +++ b/Documentation/admin-guide/sysrq.rst
> @@ -32,6 +32,7 @@ to 1. Here is the list of possible values in /proc/sys/kernel/sysrq:
> 64 = 0x40 - enable signalling of processes (term, kill, oom-kill)
> 128 = 0x80 - allow reboot/poweroff
> 256 = 0x100 - allow nicing of all RT tasks
> + 512 = 0x200 - allow compound action
>
> You can set the value in the file by the following command::
>
> @@ -148,6 +149,14 @@ Command Function
>
> ``z`` Dump the ftrace buffer
>
> +``C`` Execute a predefined, compound action. The action is defined with
> + sysrq.sysrq_compound_action module parameter, whose value contains known
> + command keys (except ``C`` to prevent recursion). The command keys can
> + be optionally followed by a colon and a number of milliseconds to wait
> + after executing the last action. For example:
> +
> + sysrq.sysrq_compound_action=r:100eis:1000ub
> +
> ``0``-``9`` Sets the console log level, controlling which kernel messages
> will be printed to your console. (``0``, for example would make
> it so that only emergency messages like PANICs or OOPSes would
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 52e344bfe8c0..ffcda1316675 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -19,6 +19,7 @@
> #include <linux/sched/rt.h>
> #include <linux/sched/debug.h>
> #include <linux/sched/task.h>
> +#include <linux/delay.h>
> #include <linux/interrupt.h>
> #include <linux/mm.h>
> #include <linux/fs.h>
> @@ -439,6 +440,15 @@ static const struct sysrq_key_op sysrq_unrt_op = {
> .enable_mask = SYSRQ_ENABLE_RTNICE,
> };
>
> +static void sysrq_action_compound(int key);
> +
> +static struct sysrq_key_op sysrq_action_compound_op = {
> + .handler = sysrq_action_compound,
> + .help_msg = "execute-compound-action(C)",
> + .action_msg = "Execute compound action",
> + .enable_mask = SYSRQ_ENABLE_COMPOUND,
> +};
> +
> /* Key Operations table and lock */
> static DEFINE_SPINLOCK(sysrq_key_table_lock);
>
> @@ -501,7 +511,7 @@ static const struct sysrq_key_op *sysrq_key_table[62] = {
> &sysrq_ftrace_dump_op, /* z */
> NULL, /* A */
> NULL, /* B */
> - NULL, /* C */
> + &sysrq_action_compound_op, /* C */
> NULL, /* D */
> NULL, /* E */
> NULL, /* F */
> @@ -634,6 +644,7 @@ EXPORT_SYMBOL(handle_sysrq);
>
> #ifdef CONFIG_INPUT
> static int sysrq_reset_downtime_ms;
> +static char *sysrq_compound_action;
>
> /* Simple translation table for the SysRq keys */
> static const unsigned char sysrq_xlate[KEY_CNT] =
> @@ -787,6 +798,61 @@ static void sysrq_of_get_keyreset_config(void)
> {
> }
> #endif
> +#define SYSRQ_COMPOUND_ACTION_VALIDATE 0
> +#define SYSRQ_COMPOUND_ACTION_RUN 1
> +
> +static int sysrq_process_compound_action(int pass)
> +{
> + const char *action = sysrq_compound_action;
> + const struct sysrq_key_op *op_p;
> + int ret, delay;
> +
> + while (*action) {
> + op_p = __sysrq_get_key_op(*action);
> + if (!op_p)
> + return -EINVAL;
> +
> + /* Don't allow calling ourselves recursively */
> + if (op_p == &sysrq_action_compound_op)
> + return -EINVAL;
> +
> + if (pass == SYSRQ_COMPOUND_ACTION_RUN)
> + __handle_sysrq(*action, false);
> +
> + if (*++action == ':') {
> + ret = sscanf(action++, ":%d", &delay);
You likely want %u and unsigned int. No negative delays.
> + if (ret < 1) /* we want at least ":[0-9]" => 1 item */
> + return -EINVAL;
> +
> + while (*action >= '0' && *action <= '9')
> + ++action;
> + if (pass == SYSRQ_COMPOUND_ACTION_RUN)
> + mdelay(delay);
> + }
> + }
> +
> + return 0;
> +}
> +
> +static void sysrq_action_compound(int key)
> +{
> + if (!sysrq_compound_action) {
> + pr_err("Unconfigured compound action for %s",
> + sysrq_action_compound_op.help_msg);
Missing \n.
> + return;
> + }
> +
> + if (sysrq_process_compound_action(SYSRQ_COMPOUND_ACTION_VALIDATE)) {
> + pr_err("Incorrect compound action %s for %s",
The same.
> + sysrq_compound_action,
> + sysrq_action_compound_op.help_msg);
> +
> + return;
> + }
> +
> + sysrq_process_compound_action(SYSRQ_COMPOUND_ACTION_RUN);
> +}
>
> static void sysrq_reinject_alt_sysrq(struct work_struct *work)
> {
> @@ -1079,8 +1145,21 @@ module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
>
> module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
>
> +module_param(sysrq_compound_action, charp, 0644);
> +MODULE_PARM_DESC(sysrq_compound_action,
> + "Compound sysrq action to be executed on Alt-Shift-SysRq-C\n"
> + "The compound action definition consists of known SysRq action letters except 'C',\n"
> + "each letter can be optionally followed by a colon and a number of milliseconds to wait\n"
> + "after executing the last action.\n"
> + "Example:\n"
> + "To unRaw, wait 100ms, tErminate, kIll, Sync, wait 1000ms, Unmount, Boot\n"
> + "sysrq.sysrq_compound_action=r:100eis:1000ub");
This looks bad in the output, use at least one \t at the start of a new
line inside the string.
--
js
suse labs
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