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linux/drivers/tty/sysrq.c
Michal Hocko c32b3cbe0d oom, PM: make OOM detection in the freezer path raceless 
Commit 5695be142e ("OOM, PM: OOM killed task shouldn't escape PM
suspend") has left a race window when OOM killer manages to
note_oom_kill after freeze_processes checks the counter.  The race
window is quite small and really unlikely and partial solution deemed
sufficient at the time of submission.

Tejun wasn't happy about this partial solution though and insisted on a
full solution.  That requires the full OOM and freezer's task freezing
exclusion, though.  This is done by this patch which introduces oom_sem
RW lock and turns oom_killer_disable() into a full OOM barrier.

oom_killer_disabled check is moved from the allocation path to the OOM
level and we take oom_sem for reading for both the check and the whole
OOM invocation.

oom_killer_disable() takes oom_sem for writing so it waits for all
currently running OOM killer invocations.  Then it disable all the further
OOMs by setting oom_killer_disabled and checks for any oom victims.
Victims are counted via mark_tsk_oom_victim resp.  unmark_oom_victim.  The
last victim wakes up all waiters enqueued by oom_killer_disable().
Therefore this function acts as the full OOM barrier.

The page fault path is covered now as well although it was assumed to be
safe before.  As per Tejun, "We used to have freezing points deep in file
system code which may be reacheable from page fault." so it would be
better and more robust to not rely on freezing points here.  Same applies
to the memcg OOM killer.

out_of_memory tells the caller whether the OOM was allowed to trigger and
the callers are supposed to handle the situation.  The page allocation
path simply fails the allocation same as before.  The page fault path will
retry the fault (more on that later) and Sysrq OOM trigger will simply
complain to the log.

Normally there wouldn't be any unfrozen user tasks after
try_to_freeze_tasks so the function will not block. But if there was an
OOM killer racing with try_to_freeze_tasks and the OOM victim didn't
finish yet then we have to wait for it. This should complete in a finite
time, though, because

	- the victim cannot loop in the page fault handler (it would die
	  on the way out from the exception)
	- it cannot loop in the page allocator because all the further
	  allocation would fail and __GFP_NOFAIL allocations are not
	  acceptable at this stage
	- it shouldn't be blocked on any locks held by frozen tasks
	  (try_to_freeze expects lockless context) and kernel threads and
	  work queues are not frozen yet

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Suggested-by: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-11 17:06:03 -08:00

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/*
* Linux Magic System Request Key Hacks
*
* (c) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
* based on ideas by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
*
* (c) 2000 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
* overhauled to use key registration
* based upon discusions in irc://irc.openprojects.net/#kernelnewbies
*
* Copyright (c) 2010 Dmitry Torokhov
* Input handler conversion
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/sched.h>
#include <linux/sched/rt.h>
#include <linux/interrupt.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/kdev_t.h>
#include <linux/major.h>
#include <linux/reboot.h>
#include <linux/sysrq.h>
#include <linux/kbd_kern.h>
#include <linux/proc_fs.h>
#include <linux/nmi.h>
#include <linux/quotaops.h>
#include <linux/perf_event.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/suspend.h>
#include <linux/writeback.h>
#include <linux/swap.h>
#include <linux/spinlock.h>
#include <linux/vt_kern.h>
#include <linux/workqueue.h>
#include <linux/hrtimer.h>
#include <linux/oom.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/uaccess.h>
#include <linux/moduleparam.h>
#include <linux/jiffies.h>
#include <linux/syscalls.h>
#include <linux/of.h>
#include <linux/rcupdate.h>
#include <asm/ptrace.h>
#include <asm/irq_regs.h>
/* Whether we react on sysrq keys or just ignore them */
static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
static bool __read_mostly sysrq_always_enabled;
unsigned short platform_sysrq_reset_seq[] __weak = { KEY_RESERVED };
int sysrq_reset_downtime_ms __weak;
static bool sysrq_on(void)
{
return sysrq_enabled || sysrq_always_enabled;
}
/*
* A value of 1 means 'all', other nonzero values are an op mask:
*/
static bool sysrq_on_mask(int mask)
{
return sysrq_always_enabled ||
sysrq_enabled == 1 ||
(sysrq_enabled & mask);
}
static int __init sysrq_always_enabled_setup(char *str)
{
sysrq_always_enabled = true;
pr_info("sysrq always enabled.\n");
return 1;
}
__setup("sysrq_always_enabled", sysrq_always_enabled_setup);
static void sysrq_handle_loglevel(int key)
{
int i;
i = key - '0';
console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
pr_info("Loglevel set to %d\n", i);
console_loglevel = i;
}
static struct sysrq_key_op sysrq_loglevel_op = {
.handler = sysrq_handle_loglevel,
.help_msg = "loglevel(0-9)",
.action_msg = "Changing Loglevel",
.enable_mask = SYSRQ_ENABLE_LOG,
};
#ifdef CONFIG_VT
static void sysrq_handle_SAK(int key)
{
struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
schedule_work(SAK_work);
}
static struct sysrq_key_op sysrq_SAK_op = {
.handler = sysrq_handle_SAK,
.help_msg = "sak(k)",
.action_msg = "SAK",
.enable_mask = SYSRQ_ENABLE_KEYBOARD,
};
#else
#define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
#endif
#ifdef CONFIG_VT
static void sysrq_handle_unraw(int key)
{
vt_reset_unicode(fg_console);
}
static struct sysrq_key_op sysrq_unraw_op = {
.handler = sysrq_handle_unraw,
.help_msg = "unraw(r)",
.action_msg = "Keyboard mode set to system default",
.enable_mask = SYSRQ_ENABLE_KEYBOARD,
};
#else
#define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
#endif /* CONFIG_VT */
static void sysrq_handle_crash(int key)
{
char *killer = NULL;
panic_on_oops = 1; /* force panic */
wmb();
*killer = 1;
}
static struct sysrq_key_op sysrq_crash_op = {
.handler = sysrq_handle_crash,
.help_msg = "crash(c)",
.action_msg = "Trigger a crash",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
static void sysrq_handle_reboot(int key)
{
lockdep_off();
local_irq_enable();
emergency_restart();
}
static struct sysrq_key_op sysrq_reboot_op = {
.handler = sysrq_handle_reboot,
.help_msg = "reboot(b)",
.action_msg = "Resetting",
.enable_mask = SYSRQ_ENABLE_BOOT,
};
static void sysrq_handle_sync(int key)
{
emergency_sync();
}
static struct sysrq_key_op sysrq_sync_op = {
.handler = sysrq_handle_sync,
.help_msg = "sync(s)",
.action_msg = "Emergency Sync",
.enable_mask = SYSRQ_ENABLE_SYNC,
};
static void sysrq_handle_show_timers(int key)
{
sysrq_timer_list_show();
}
static struct sysrq_key_op sysrq_show_timers_op = {
.handler = sysrq_handle_show_timers,
.help_msg = "show-all-timers(q)",
.action_msg = "Show clockevent devices & pending hrtimers (no others)",
};
static void sysrq_handle_mountro(int key)
{
emergency_remount();
}
static struct sysrq_key_op sysrq_mountro_op = {
.handler = sysrq_handle_mountro,
.help_msg = "unmount(u)",
.action_msg = "Emergency Remount R/O",
.enable_mask = SYSRQ_ENABLE_REMOUNT,
};
#ifdef CONFIG_LOCKDEP
static void sysrq_handle_showlocks(int key)
{
debug_show_all_locks();
}
static struct sysrq_key_op sysrq_showlocks_op = {
.handler = sysrq_handle_showlocks,
.help_msg = "show-all-locks(d)",
.action_msg = "Show Locks Held",
};
#else
#define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
#endif
#ifdef CONFIG_SMP
static DEFINE_SPINLOCK(show_lock);
static void showacpu(void *dummy)
{
unsigned long flags;
/* Idle CPUs have no interesting backtrace. */
if (idle_cpu(smp_processor_id()))
return;
spin_lock_irqsave(&show_lock, flags);
pr_info("CPU%d:\n", smp_processor_id());
show_stack(NULL, NULL);
spin_unlock_irqrestore(&show_lock, flags);
}
static void sysrq_showregs_othercpus(struct work_struct *dummy)
{
smp_call_function(showacpu, NULL, 0);
}
static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
static void sysrq_handle_showallcpus(int key)
{
/*
* Fall back to the workqueue based printing if the
* backtrace printing did not succeed or the
* architecture has no support for it:
*/
if (!trigger_all_cpu_backtrace()) {
struct pt_regs *regs = get_irq_regs();
if (regs) {
pr_info("CPU%d:\n", smp_processor_id());
show_regs(regs);
}
schedule_work(&sysrq_showallcpus);
}
}
static struct sysrq_key_op sysrq_showallcpus_op = {
.handler = sysrq_handle_showallcpus,
.help_msg = "show-backtrace-all-active-cpus(l)",
.action_msg = "Show backtrace of all active CPUs",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
#endif
static void sysrq_handle_showregs(int key)
{
struct pt_regs *regs = get_irq_regs();
if (regs)
show_regs(regs);
perf_event_print_debug();
}
static struct sysrq_key_op sysrq_showregs_op = {
.handler = sysrq_handle_showregs,
.help_msg = "show-registers(p)",
.action_msg = "Show Regs",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
static void sysrq_handle_showstate(int key)
{
show_state();
}
static struct sysrq_key_op sysrq_showstate_op = {
.handler = sysrq_handle_showstate,
.help_msg = "show-task-states(t)",
.action_msg = "Show State",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
static void sysrq_handle_showstate_blocked(int key)
{
show_state_filter(TASK_UNINTERRUPTIBLE);
}
static struct sysrq_key_op sysrq_showstate_blocked_op = {
.handler = sysrq_handle_showstate_blocked,
.help_msg = "show-blocked-tasks(w)",
.action_msg = "Show Blocked State",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
#ifdef CONFIG_TRACING
#include <linux/ftrace.h>
static void sysrq_ftrace_dump(int key)
{
ftrace_dump(DUMP_ALL);
}
static struct sysrq_key_op sysrq_ftrace_dump_op = {
.handler = sysrq_ftrace_dump,
.help_msg = "dump-ftrace-buffer(z)",
.action_msg = "Dump ftrace buffer",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
#else
#define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
#endif
static void sysrq_handle_showmem(int key)
{
show_mem(0);
}
static struct sysrq_key_op sysrq_showmem_op = {
.handler = sysrq_handle_showmem,
.help_msg = "show-memory-usage(m)",
.action_msg = "Show Memory",
.enable_mask = SYSRQ_ENABLE_DUMP,
};
/*
* Signal sysrq helper function. Sends a signal to all user processes.
*/
static void send_sig_all(int sig)
{
struct task_struct *p;
read_lock(&tasklist_lock);
for_each_process(p) {
if (p->flags & PF_KTHREAD)
continue;
if (is_global_init(p))
continue;
do_send_sig_info(sig, SEND_SIG_FORCED, p, true);
}
read_unlock(&tasklist_lock);
}
static void sysrq_handle_term(int key)
{
send_sig_all(SIGTERM);
console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
}
static struct sysrq_key_op sysrq_term_op = {
.handler = sysrq_handle_term,
.help_msg = "terminate-all-tasks(e)",
.action_msg = "Terminate All Tasks",
.enable_mask = SYSRQ_ENABLE_SIGNAL,
};
static void moom_callback(struct work_struct *ignored)
{
if (!out_of_memory(node_zonelist(first_memory_node, GFP_KERNEL),
GFP_KERNEL, 0, NULL, true))
pr_info("OOM request ignored because killer is disabled\n");
}
static DECLARE_WORK(moom_work, moom_callback);
static void sysrq_handle_moom(int key)
{
schedule_work(&moom_work);
}
static struct sysrq_key_op sysrq_moom_op = {
.handler = sysrq_handle_moom,
.help_msg = "memory-full-oom-kill(f)",
.action_msg = "Manual OOM execution",
.enable_mask = SYSRQ_ENABLE_SIGNAL,
};
#ifdef CONFIG_BLOCK
static void sysrq_handle_thaw(int key)
{
emergency_thaw_all();
}
static struct sysrq_key_op sysrq_thaw_op = {
.handler = sysrq_handle_thaw,
.help_msg = "thaw-filesystems(j)",
.action_msg = "Emergency Thaw of all frozen filesystems",
.enable_mask = SYSRQ_ENABLE_SIGNAL,
};
#endif
static void sysrq_handle_kill(int key)
{
send_sig_all(SIGKILL);
console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
}
static struct sysrq_key_op sysrq_kill_op = {
.handler = sysrq_handle_kill,
.help_msg = "kill-all-tasks(i)",
.action_msg = "Kill All Tasks",
.enable_mask = SYSRQ_ENABLE_SIGNAL,
};
static void sysrq_handle_unrt(int key)
{
normalize_rt_tasks();
}
static struct sysrq_key_op sysrq_unrt_op = {
.handler = sysrq_handle_unrt,
.help_msg = "nice-all-RT-tasks(n)",
.action_msg = "Nice All RT Tasks",
.enable_mask = SYSRQ_ENABLE_RTNICE,
};
/* Key Operations table and lock */
static DEFINE_SPINLOCK(sysrq_key_table_lock);
static struct sysrq_key_op *sysrq_key_table[36] = {
&sysrq_loglevel_op, /* 0 */
&sysrq_loglevel_op, /* 1 */
&sysrq_loglevel_op, /* 2 */
&sysrq_loglevel_op, /* 3 */
&sysrq_loglevel_op, /* 4 */
&sysrq_loglevel_op, /* 5 */
&sysrq_loglevel_op, /* 6 */
&sysrq_loglevel_op, /* 7 */
&sysrq_loglevel_op, /* 8 */
&sysrq_loglevel_op, /* 9 */
/*
* a: Don't use for system provided sysrqs, it is handled specially on
* sparc and will never arrive.
*/
NULL, /* a */
&sysrq_reboot_op, /* b */
&sysrq_crash_op, /* c & ibm_emac driver debug */
&sysrq_showlocks_op, /* d */
&sysrq_term_op, /* e */
&sysrq_moom_op, /* f */
/* g: May be registered for the kernel debugger */
NULL, /* g */
NULL, /* h - reserved for help */
&sysrq_kill_op, /* i */
#ifdef CONFIG_BLOCK
&sysrq_thaw_op, /* j */
#else
NULL, /* j */
#endif
&sysrq_SAK_op, /* k */
#ifdef CONFIG_SMP
&sysrq_showallcpus_op, /* l */
#else
NULL, /* l */
#endif
&sysrq_showmem_op, /* m */
&sysrq_unrt_op, /* n */
/* o: This will often be registered as 'Off' at init time */
NULL, /* o */
&sysrq_showregs_op, /* p */
&sysrq_show_timers_op, /* q */
&sysrq_unraw_op, /* r */
&sysrq_sync_op, /* s */
&sysrq_showstate_op, /* t */
&sysrq_mountro_op, /* u */
/* v: May be registered for frame buffer console restore */
NULL, /* v */
&sysrq_showstate_blocked_op, /* w */
/* x: May be registered on ppc/powerpc for xmon */
/* x: May be registered on sparc64 for global PMU dump */
NULL, /* x */
/* y: May be registered on sparc64 for global register dump */
NULL, /* y */
&sysrq_ftrace_dump_op, /* z */
};
/* key2index calculation, -1 on invalid index */
static int sysrq_key_table_key2index(int key)
{
int retval;
if ((key >= '0') && (key <= '9'))
retval = key - '0';
else if ((key >= 'a') && (key <= 'z'))
retval = key + 10 - 'a';
else
retval = -1;
return retval;
}
/*
* get and put functions for the table, exposed to modules.
*/
struct sysrq_key_op *__sysrq_get_key_op(int key)
{
struct sysrq_key_op *op_p = NULL;
int i;
i = sysrq_key_table_key2index(key);
if (i != -1)
op_p = sysrq_key_table[i];
return op_p;
}
static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
{
int i = sysrq_key_table_key2index(key);
if (i != -1)
sysrq_key_table[i] = op_p;
}
void __handle_sysrq(int key, bool check_mask)
{
struct sysrq_key_op *op_p;
int orig_log_level;
int i;
rcu_sysrq_start();
rcu_read_lock();
/*
* Raise the apparent loglevel to maximum so that the sysrq header
* is shown to provide the user with positive feedback. We do not
* simply emit this at KERN_EMERG as that would change message
* routing in the consumers of /proc/kmsg.
*/
orig_log_level = console_loglevel;
console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
pr_info("SysRq : ");
op_p = __sysrq_get_key_op(key);
if (op_p) {
/*
* Should we check for enabled operations (/proc/sysrq-trigger
* should not) and is the invoked operation enabled?
*/
if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
pr_cont("%s\n", op_p->action_msg);
console_loglevel = orig_log_level;
op_p->handler(key);
} else {
pr_cont("This sysrq operation is disabled.\n");
}
} else {
pr_cont("HELP : ");
/* Only print the help msg once per handler */
for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
if (sysrq_key_table[i]) {
int j;
for (j = 0; sysrq_key_table[i] !=
sysrq_key_table[j]; j++)
;
if (j != i)
continue;
pr_cont("%s ", sysrq_key_table[i]->help_msg);
}
}
pr_cont("\n");
console_loglevel = orig_log_level;
}
rcu_read_unlock();
rcu_sysrq_end();
}
void handle_sysrq(int key)
{
if (sysrq_on())
__handle_sysrq(key, true);
}
EXPORT_SYMBOL(handle_sysrq);
#ifdef CONFIG_INPUT
/* Simple translation table for the SysRq keys */
static const unsigned char sysrq_xlate[KEY_CNT] =
"\000\0331234567890-=\177\t" /* 0x00 - 0x0f */
"qwertyuiop[]\r\000as" /* 0x10 - 0x1f */
"dfghjkl;'`\000\\zxcv" /* 0x20 - 0x2f */
"bnm,./\000*\000 \000\201\202\203\204\205" /* 0x30 - 0x3f */
"\206\207\210\211\212\000\000789-456+1" /* 0x40 - 0x4f */
"230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
"\r\000/"; /* 0x60 - 0x6f */
struct sysrq_state {
struct input_handle handle;
struct work_struct reinject_work;
unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
unsigned int alt;
unsigned int alt_use;
bool active;
bool need_reinject;
bool reinjecting;
/* reset sequence handling */
bool reset_canceled;
bool reset_requested;
unsigned long reset_keybit[BITS_TO_LONGS(KEY_CNT)];
int reset_seq_len;
int reset_seq_cnt;
int reset_seq_version;
struct timer_list keyreset_timer;
};
#define SYSRQ_KEY_RESET_MAX 20 /* Should be plenty */
static unsigned short sysrq_reset_seq[SYSRQ_KEY_RESET_MAX];
static unsigned int sysrq_reset_seq_len;
static unsigned int sysrq_reset_seq_version = 1;
static void sysrq_parse_reset_sequence(struct sysrq_state *state)
{
int i;
unsigned short key;
state->reset_seq_cnt = 0;
for (i = 0; i < sysrq_reset_seq_len; i++) {
key = sysrq_reset_seq[i];
if (key == KEY_RESERVED || key > KEY_MAX)
break;
__set_bit(key, state->reset_keybit);
state->reset_seq_len++;
if (test_bit(key, state->key_down))
state->reset_seq_cnt++;
}
/* Disable reset until old keys are not released */
state->reset_canceled = state->reset_seq_cnt != 0;
state->reset_seq_version = sysrq_reset_seq_version;
}
static void sysrq_do_reset(unsigned long _state)
{
struct sysrq_state *state = (struct sysrq_state *) _state;
state->reset_requested = true;
sys_sync();
kernel_restart(NULL);
}
static void sysrq_handle_reset_request(struct sysrq_state *state)
{
if (state->reset_requested)
__handle_sysrq(sysrq_xlate[KEY_B], false);
if (sysrq_reset_downtime_ms)
mod_timer(&state->keyreset_timer,
jiffies + msecs_to_jiffies(sysrq_reset_downtime_ms));
else
sysrq_do_reset((unsigned long)state);
}
static void sysrq_detect_reset_sequence(struct sysrq_state *state,
unsigned int code, int value)
{
if (!test_bit(code, state->reset_keybit)) {
/*
* Pressing any key _not_ in reset sequence cancels
* the reset sequence. Also cancelling the timer in
* case additional keys were pressed after a reset
* has been requested.
*/
if (value && state->reset_seq_cnt) {
state->reset_canceled = true;
del_timer(&state->keyreset_timer);
}
} else if (value == 0) {
/*
* Key release - all keys in the reset sequence need
* to be pressed and held for the reset timeout
* to hold.
*/
del_timer(&state->keyreset_timer);
if (--state->reset_seq_cnt == 0)
state->reset_canceled = false;
} else if (value == 1) {
/* key press, not autorepeat */
if (++state->reset_seq_cnt == state->reset_seq_len &&
!state->reset_canceled) {
sysrq_handle_reset_request(state);
}
}
}
#ifdef CONFIG_OF
static void sysrq_of_get_keyreset_config(void)
{
u32 key;
struct device_node *np;
struct property *prop;
const __be32 *p;
np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
if (!np) {
pr_debug("No sysrq node found");
return;
}
/* Reset in case a __weak definition was present */
sysrq_reset_seq_len = 0;
of_property_for_each_u32(np, "keyset", prop, p, key) {
if (key == KEY_RESERVED || key > KEY_MAX ||
sysrq_reset_seq_len == SYSRQ_KEY_RESET_MAX)
break;
sysrq_reset_seq[sysrq_reset_seq_len++] = (unsigned short)key;
}
/* Get reset timeout if any. */
of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
}
#else
static void sysrq_of_get_keyreset_config(void)
{
}
#endif
static void sysrq_reinject_alt_sysrq(struct work_struct *work)
{
struct sysrq_state *sysrq =
container_of(work, struct sysrq_state, reinject_work);
struct input_handle *handle = &sysrq->handle;
unsigned int alt_code = sysrq->alt_use;
if (sysrq->need_reinject) {
/* we do not want the assignment to be reordered */
sysrq->reinjecting = true;
mb();
/* Simulate press and release of Alt + SysRq */
input_inject_event(handle, EV_KEY, alt_code, 1);
input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
input_inject_event(handle, EV_KEY, alt_code, 0);
input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
mb();
sysrq->reinjecting = false;
}
}
static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
unsigned int code, int value)
{
bool was_active = sysrq->active;
bool suppress;
switch (code) {
case KEY_LEFTALT:
case KEY_RIGHTALT:
if (!value) {
/* One of ALTs is being released */
if (sysrq->active && code == sysrq->alt_use)
sysrq->active = false;
sysrq->alt = KEY_RESERVED;
} else if (value != 2) {
sysrq->alt = code;
sysrq->need_reinject = false;
}
break;
case KEY_SYSRQ:
if (value == 1 && sysrq->alt != KEY_RESERVED) {
sysrq->active = true;
sysrq->alt_use = sysrq->alt;
/*
* If nothing else will be pressed we'll need
* to re-inject Alt-SysRq keysroke.
*/
sysrq->need_reinject = true;
}
/*
* Pretend that sysrq was never pressed at all. This
* is needed to properly handle KGDB which will try
* to release all keys after exiting debugger. If we
* do not clear key bit it KGDB will end up sending
* release events for Alt and SysRq, potentially
* triggering print screen function.
*/
if (sysrq->active)
clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);
break;
default:
if (sysrq->active && value && value != 2) {
sysrq->need_reinject = false;
__handle_sysrq(sysrq_xlate[code], true);
}
break;
}
suppress = sysrq->active;
if (!sysrq->active) {
/*
* See if reset sequence has changed since the last time.
*/
if (sysrq->reset_seq_version != sysrq_reset_seq_version)
sysrq_parse_reset_sequence(sysrq);
/*
* If we are not suppressing key presses keep track of
* keyboard state so we can release keys that have been
* pressed before entering SysRq mode.
*/
if (value)
set_bit(code, sysrq->key_down);
else
clear_bit(code, sysrq->key_down);
if (was_active)
schedule_work(&sysrq->reinject_work);
/* Check for reset sequence */
sysrq_detect_reset_sequence(sysrq, code, value);
} else if (value == 0 && test_and_clear_bit(code, sysrq->key_down)) {
/*
* Pass on release events for keys that was pressed before
* entering SysRq mode.
*/
suppress = false;
}
return suppress;
}
static bool sysrq_filter(struct input_handle *handle,
unsigned int type, unsigned int code, int value)
{
struct sysrq_state *sysrq = handle->private;
bool suppress;
/*
* Do not filter anything if we are in the process of re-injecting
* Alt+SysRq combination.
*/
if (sysrq->reinjecting)
return false;
switch (type) {
case EV_SYN:
suppress = false;
break;
case EV_KEY:
suppress = sysrq_handle_keypress(sysrq, code, value);
break;
default:
suppress = sysrq->active;
break;
}
return suppress;
}
static int sysrq_connect(struct input_handler *handler,
struct input_dev *dev,
const struct input_device_id *id)
{
struct sysrq_state *sysrq;
int error;
sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
if (!sysrq)
return -ENOMEM;
INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
sysrq->handle.dev = dev;
sysrq->handle.handler = handler;
sysrq->handle.name = "sysrq";
sysrq->handle.private = sysrq;
setup_timer(&sysrq->keyreset_timer,
sysrq_do_reset, (unsigned long)sysrq);
error = input_register_handle(&sysrq->handle);
if (error) {
pr_err("Failed to register input sysrq handler, error %d\n",
error);
goto err_free;
}
error = input_open_device(&sysrq->handle);
if (error) {
pr_err("Failed to open input device, error %d\n", error);
goto err_unregister;
}
return 0;
err_unregister:
input_unregister_handle(&sysrq->handle);
err_free:
kfree(sysrq);
return error;
}
static void sysrq_disconnect(struct input_handle *handle)
{
struct sysrq_state *sysrq = handle->private;
input_close_device(handle);
cancel_work_sync(&sysrq->reinject_work);
del_timer_sync(&sysrq->keyreset_timer);
input_unregister_handle(handle);
kfree(sysrq);
}
/*
* We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
* keyboards have SysRq key predefined and so user may add it to keymap
* later, but we expect all such keyboards to have left alt.
*/
static const struct input_device_id sysrq_ids[] = {
{
.flags = INPUT_DEVICE_ID_MATCH_EVBIT |
INPUT_DEVICE_ID_MATCH_KEYBIT,
.evbit = { BIT_MASK(EV_KEY) },
.keybit = { BIT_MASK(KEY_LEFTALT) },
},
{ },
};
static struct input_handler sysrq_handler = {
.filter = sysrq_filter,
.connect = sysrq_connect,
.disconnect = sysrq_disconnect,
.name = "sysrq",
.id_table = sysrq_ids,
};
static bool sysrq_handler_registered;
static inline void sysrq_register_handler(void)
{
unsigned short key;
int error;
int i;
/* First check if a __weak interface was instantiated. */
for (i = 0; i < ARRAY_SIZE(sysrq_reset_seq); i++) {
key = platform_sysrq_reset_seq[i];
if (key == KEY_RESERVED || key > KEY_MAX)
break;
sysrq_reset_seq[sysrq_reset_seq_len++] = key;
}
/*
* DT configuration takes precedence over anything that would
* have been defined via the __weak interface.
*/
sysrq_of_get_keyreset_config();
error = input_register_handler(&sysrq_handler);
if (error)
pr_err("Failed to register input handler, error %d", error);
else
sysrq_handler_registered = true;
}
static inline void sysrq_unregister_handler(void)
{
if (sysrq_handler_registered) {
input_unregister_handler(&sysrq_handler);
sysrq_handler_registered = false;
}
}
static int sysrq_reset_seq_param_set(const char *buffer,
const struct kernel_param *kp)
{
unsigned long val;
int error;
error = kstrtoul(buffer, 0, &val);
if (error < 0)
return error;
if (val > KEY_MAX)
return -EINVAL;
*((unsigned short *)kp->arg) = val;
sysrq_reset_seq_version++;
return 0;
}
static struct kernel_param_ops param_ops_sysrq_reset_seq = {
.get = param_get_ushort,
.set = sysrq_reset_seq_param_set,
};
#define param_check_sysrq_reset_seq(name, p) \
__param_check(name, p, unsigned short)
module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
&sysrq_reset_seq_len, 0644);
module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
#else
static inline void sysrq_register_handler(void)
{
}
static inline void sysrq_unregister_handler(void)
{
}
#endif /* CONFIG_INPUT */
int sysrq_toggle_support(int enable_mask)
{
bool was_enabled = sysrq_on();
sysrq_enabled = enable_mask;
if (was_enabled != sysrq_on()) {
if (sysrq_on())
sysrq_register_handler();
else
sysrq_unregister_handler();
}
return 0;
}
static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
struct sysrq_key_op *remove_op_p)
{
int retval;
spin_lock(&sysrq_key_table_lock);
if (__sysrq_get_key_op(key) == remove_op_p) {
__sysrq_put_key_op(key, insert_op_p);
retval = 0;
} else {
retval = -1;
}
spin_unlock(&sysrq_key_table_lock);
/*
* A concurrent __handle_sysrq either got the old op or the new op.
* Wait for it to go away before returning, so the code for an old
* op is not freed (eg. on module unload) while it is in use.
*/
synchronize_rcu();
return retval;
}
int register_sysrq_key(int key, struct sysrq_key_op *op_p)
{
return __sysrq_swap_key_ops(key, op_p, NULL);
}
EXPORT_SYMBOL(register_sysrq_key);
int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
{
return __sysrq_swap_key_ops(key, NULL, op_p);
}
EXPORT_SYMBOL(unregister_sysrq_key);
#ifdef CONFIG_PROC_FS
/*
* writing 'C' to /proc/sysrq-trigger is like sysrq-C
*/
static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
if (count) {
char c;
if (get_user(c, buf))
return -EFAULT;
__handle_sysrq(c, false);
}
return count;
}
static const struct file_operations proc_sysrq_trigger_operations = {
.write = write_sysrq_trigger,
.llseek = noop_llseek,
};
static void sysrq_init_procfs(void)
{
if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
&proc_sysrq_trigger_operations))
pr_err("Failed to register proc interface\n");
}
#else
static inline void sysrq_init_procfs(void)
{
}
#endif /* CONFIG_PROC_FS */
static int __init sysrq_init(void)
{
sysrq_init_procfs();
if (sysrq_on())
sysrq_register_handler();
return 0;
}
module_init(sysrq_init);
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