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Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk

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Pull printk updates from Petr Mladek:

 - There is a situation when early console is not deregistered because
   the preferred one matches a wrong entry. It caused messages to appear
   twice.

   This is the 2nd attempt to fix it. The first one was wrong, see the
   commit c6c7d83b9c ('Revert "console: don't prefer first registered
   if DT specifies stdout-path"').

   The fix is coupled with some small code clean up. Well, the console
   registration code would deserve a big one. We need to think about it.

 - Do not lose information about the preemtive context when the console
   semaphore is re-taken.

 - Do not block CPU hotplug when someone else is already pushing
   messages to the console.

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk:
  printk: fix double printing with earlycon
  printk: rename selected_console -> preferred_console
  printk: fix name/type/scope of preferred_console var
  printk: Correctly handle preemption in console_unlock()
  printk: use console_trylock() in console_cpu_notify()
This commit is contained in:
Linus Torvalds 2017-05-03 18:29:28 -07:00
commit 9c35baf6ce
1 changed files with 56 additions and 25 deletions
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81
kernel/printk/printk.c
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@ -269,8 +269,8 @@ static struct console *exclusive_console;
#define MAX_CMDLINECONSOLES 8
static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
static int console_cmdline_cnt;
static int selected_console = -1;
static int preferred_console = -1;
int console_set_on_cmdline;
EXPORT_SYMBOL(console_set_on_cmdline);
@ -1906,24 +1906,38 @@ static int __add_preferred_console(char *name, int idx, char *options,
* See if this tty is not yet registered, and
* if we have a slot free.
*/
for (i = 0, c = console_cmdline;
i < MAX_CMDLINECONSOLES && c->name[0];
i++, c++) {
for (i = 0, c = console_cmdline; i < console_cmdline_cnt; i++, c++) {
if (strcmp(c->name, name) == 0 && c->index == idx) {
if (!brl_options)
selected_console = i;
if (brl_options)
return 0;
/*
* Maintain an invariant that will help to find if
* the matching console is preferred, see
* register_console():
*
* The last non-braille console is always
* the preferred one.
*/
if (i != console_cmdline_cnt - 1)
swap(console_cmdline[i],
console_cmdline[console_cmdline_cnt - 1]);
preferred_console = console_cmdline_cnt - 1;
return 0;
}
}
if (i == MAX_CMDLINECONSOLES)
return -E2BIG;
if (!brl_options)
selected_console = i;
preferred_console = i;
strlcpy(c->name, name, sizeof(c->name));
c->options = options;
braille_set_options(c, brl_options);
c->index = idx;
console_cmdline_cnt++;
return 0;
}
/*
@ -2031,15 +2045,16 @@ void resume_console(void)
* @cpu: unused
*
* If printk() is called from a CPU that is not online yet, the messages
* will be spooled but will not show up on the console. This function is
* called when a new CPU comes online (or fails to come up), and ensures
* that any such output gets printed.
* will be printed on the console only if there are CON_ANYTIME consoles.
* This function is called when a new CPU comes online (or fails to come
* up) or goes offline.
*/
static int console_cpu_notify(unsigned int cpu)
{
if (!cpuhp_tasks_frozen) {
console_lock();
console_unlock();
/* If trylock fails, someone else is doing the printing */
if (console_trylock())
console_unlock();
}
return 0;
}
@ -2161,7 +2176,7 @@ void console_unlock(void)
}
/*
* Console drivers are called under logbuf_lock, so
* Console drivers are called with interrupts disabled, so
* @console_may_schedule should be cleared before; however, we may
* end up dumping a lot of lines, for example, if called from
* console registration path, and should invoke cond_resched()
@ -2169,11 +2184,15 @@ void console_unlock(void)
* scheduling stall on a slow console leading to RCU stall and
* softlockup warnings which exacerbate the issue with more
* messages practically incapacitating the system.
*
* console_trylock() is not able to detect the preemptive
* context reliably. Therefore the value must be stored before
* and cleared after the the "again" goto label.
*/
do_cond_resched = console_may_schedule;
again:
console_may_schedule = 0;
again:
/*
* We released the console_sem lock, so we need to recheck if
* cpu is online and (if not) is there at least one CON_ANYTIME
@ -2409,6 +2428,7 @@ void register_console(struct console *newcon)
unsigned long flags;
struct console *bcon = NULL;
struct console_cmdline *c;
static bool has_preferred;
if (console_drivers)
for_each_console(bcon)
@ -2435,15 +2455,15 @@ void register_console(struct console *newcon)
if (console_drivers && console_drivers->flags & CON_BOOT)
bcon = console_drivers;
if (preferred_console < 0 || bcon || !console_drivers)
preferred_console = selected_console;
if (!has_preferred || bcon || !console_drivers)
has_preferred = preferred_console >= 0;
/*
* See if we want to use this console driver. If we
* didn't select a console we take the first one
* that registers here.
*/
if (preferred_console < 0) {
if (!has_preferred) {
if (newcon->index < 0)
newcon->index = 0;
if (newcon->setup == NULL ||
@ -2451,18 +2471,29 @@ void register_console(struct console *newcon)
newcon->flags |= CON_ENABLED;
if (newcon->device) {
newcon->flags |= CON_CONSDEV;
preferred_console = 0;
has_preferred = true;
}
}
}
/*
* See if this console matches one we selected on
* the command line.
* See if this console matches one we selected on the command line.
*
* There may be several entries in the console_cmdline array matching
* with the same console, one with newcon->match(), another by
* name/index:
*
* pl011,mmio,0x87e024000000,115200 -- added from SPCR
* ttyAMA0 -- added from command line
*
* Traverse the console_cmdline array in reverse order to be
* sure that if this console is preferred then it will be the first
* matching entry. We use the invariant that is maintained in
* __add_preferred_console().
*/
for (i = 0, c = console_cmdline;
i < MAX_CMDLINECONSOLES && c->name[0];
i++, c++) {
for (i = console_cmdline_cnt - 1; i >= 0; i--) {
c = console_cmdline + i;
if (!newcon->match ||
newcon->match(newcon, c->name, c->index, c->options) != 0) {
/* default matching */
@ -2484,9 +2515,9 @@ void register_console(struct console *newcon)
}
newcon->flags |= CON_ENABLED;
if (i == selected_console) {
if (i == preferred_console) {
newcon->flags |= CON_CONSDEV;
preferred_console = selected_console;
has_preferred = true;
}
break;
}