+CC Buildroot folks
Hi Petr,
On 11/11/20 5:54 AM, Petr Mladek wrote:
stdin, stdout, and stderr standard I/O stream are created for the init
process. They are not available when there is no console registered
for /dev/console. It might lead to a crash when the init process
tries to use them, see the commit 48021f98130880dd742 ("printk: handle
blank console arguments passed in.").
Normally, ttySX and ttyX consoles are used as a fallback when no consoles
are defined via the command line, device tree, or SPCR. But there
will be no console registered when an invalid console name is configured
or when the configured consoles do not exist on the system.
Users even try to avoid the console intentionally, for example,
by using console="" or console=null. It is used on production
systems where the serial port or terminal are not visible to
users. Pushing messages to these consoles would just unnecessary
slowdown the system.
Make sure that stdin, stdout, stderr, and /dev/console are always
available by a fallback to the existing ttynull driver. It has
been implemented for exactly this purpose but it was used only
when explicitly configured.
Signed-off-by: Petr Mladek
--- a/init/main.c
+++ b/init/main.c
@@ -1470,8 +1470,14 @@ void __init console_on_rootfs(void)
struct file *file = filp_open("/dev/console", O_RDWR, 0);
if (IS_ERR(file)) {
- pr_err("Warning: unable to open an initial console.\n");
- return;
+ pr_err("Warning: unable to open an initial console. Fallback to
ttynull.\n");
+ register_ttynull_console();
+
+ file = filp_open("/dev/console", O_RDWR, 0);
+ if (IS_ERR(file)) {
+ pr_err("Warning: Failed to add ttynull console. No stdin,
stdout, and stderr for the init process!\n");
+ return;
+ }
This breaks ARC booting (no output on console).
Our Buildroot based setup has dynamic /dev where /dev/console doesn't
exist statically and there's a primoridla /init shell script which does
following
/bin/mount -t devtmpfs devtmpfs /dev
exec 0/dev/console
exec 2>/dev/console
exec /sbin/init "$@"
Buildroot has had this way of handling missing /dev/console since 2011
[1] and [2].
Please advise what needs to be done to unbork boot. Otherwise this seems
like a kernel change which breaks user-space and needs to be backed-out
(or perhaps conditionalize on CONFIG_NULL_TTY. I'm surprised it hasn't
been reported by any other embedded folks
Thx,
-Vineet
[1] http://lists.busybox.net/pipermail/buildroot/2011-July/044505.html
[2] http://lists.busybox.net/pipermail/buildroot/2011-August/044832.html
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