Commit 7bf693951a8e5f7e600a45b74d91d962a453146e
Committed by
Linus Torvalds
Linus Torvalds
1 parent
26297607e0
Exists in
master
and in
4 other branches
console: allow to retain boot console via boot option keep_bootcon
On some architectures, the boot process involves de-registering the boot console (early boot), initialize drivers and then re-register the console. This mechanism introduces a window in which no printk can happen on the console and messages are buffered and then printed once the new console is available. If a kernel crashes during this window, all it's left on the boot console is "console [foo] enabled, bootconsole disabled" making debug of the crash rather 'interesting'. By adding "keep_bootcon" option, do not unregister the boot console, that will allow to printk everything that is happening up to the crash. The option is clearly meant only for debugging purposes as it introduces lots of duplicated info printed on console, but will make bug report from users easier as it doesn't require a kernel build just to figure out where we crash. Signed-off-by: Fabio M. Di Nitto <fabbione@fabbione.net> Acked-by: David S. Miller <davem@davemloft.net> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Greg KH <gregkh@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Showing 2 changed files with 21 additions and 1 deletions Side-by-side Diff
Documentation/kernel-parameters.txt
| ... | ... | @@ -872,6 +872,12 @@ |
| 872 | 872 | If specified, z/VM IUCV HVC accepts connections |
| 873 | 873 | from listed z/VM user IDs only. |
| 874 | 874 | |
| 875 | + keep_bootcon [KNL] | |
| 876 | + Do not unregister boot console at start. This is only | |
| 877 | + useful for debugging when something happens in the window | |
| 878 | + between unregistering the boot console and initializing | |
| 879 | + the real console. | |
| 880 | + | |
| 875 | 881 | i2c_bus= [HW] Override the default board specific I2C bus speed |
| 876 | 882 | or register an additional I2C bus that is not |
| 877 | 883 | registered from board initialization code. |
kernel/printk.c
| ... | ... | @@ -1316,6 +1316,18 @@ |
| 1316 | 1316 | } |
| 1317 | 1317 | EXPORT_SYMBOL(console_start); |
| 1318 | 1318 | |
| 1319 | +static int __read_mostly keep_bootcon; | |
| 1320 | + | |
| 1321 | +static int __init keep_bootcon_setup(char *str) | |
| 1322 | +{ | |
| 1323 | + keep_bootcon = 1; | |
| 1324 | + printk(KERN_INFO "debug: skip boot console de-registration.\n"); | |
| 1325 | + | |
| 1326 | + return 0; | |
| 1327 | +} | |
| 1328 | + | |
| 1329 | +early_param("keep_bootcon", keep_bootcon_setup); | |
| 1330 | + | |
| 1319 | 1331 | /* |
| 1320 | 1332 | * The console driver calls this routine during kernel initialization |
| 1321 | 1333 | * to register the console printing procedure with printk() and to |
| ... | ... | @@ -1463,7 +1475,9 @@ |
| 1463 | 1475 | * users know there might be something in the kernel's log buffer that |
| 1464 | 1476 | * went to the bootconsole (that they do not see on the real console) |
| 1465 | 1477 | */ |
| 1466 | - if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) { | |
| 1478 | + if (bcon && | |
| 1479 | + ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) && | |
| 1480 | + !keep_bootcon) { | |
| 1467 | 1481 | /* we need to iterate through twice, to make sure we print |
| 1468 | 1482 | * everything out, before we unregister the console(s) |
| 1469 | 1483 | */ |