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author | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2020-02-13 10:51:32 +0100 |
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committer | Petr Mladek <pmladek@suse.com> | 2020-02-18 09:34:42 +0100 |
commit | e369d8227fd211be36242fc44a9dc2209e246b9a (patch) | |
tree | 32a712fee0f28645ea31104759119ed73e5bf4b9 /kernel/printk/console_cmdline.h | |
parent | ad8cd1db80cc33337bdbee63c453ef6d5132474b (diff) | |
download | linux-e369d8227fd211be36242fc44a9dc2209e246b9a.tar.gz linux-e369d8227fd211be36242fc44a9dc2209e246b9a.tar.bz2 linux-e369d8227fd211be36242fc44a9dc2209e246b9a.zip |
printk: Fix preferred console selection with multiple matches
In the following circumstances, the rule of selecting the console
corresponding to the last "console=" entry on the command line as
the preferred console (CON_CONSDEV, ie, /dev/console) fails. This
is a specific example, but it could happen with different consoles
that have a similar name aliasing mechanism.
- The kernel command line has both console=tty0 and console=ttyS0
in that order (the latter with speed etc... arguments).
This is common with some cloud setups such as Amazon Linux.
- add_preferred_console is called early to register "uart0". In
our case that happens from acpi_parse_spcr() on arm64 since the
"enable_console" argument is true on that architecture. This causes
"uart0" to become entry 0 of the console_cmdline array.
Now, because of the above, what happens is:
- add_preferred_console is called by the cmdline parsing for tty0
and ttyS0 respectively, thus occupying entries 1 and 2 of the
console_cmdline array (since this happens after ACPI SPCR parsing).
At that point preferred_console is set to 2 as expected.
- When the tty layer kicks in, it will call register_console for tty0.
This will match entry 1 in console_cmdline array. It isn't our
preferred console but because it's our only console at this point,
it will end up "first" in the consoles list.
- When 8250 probes the actual serial port later on, it calls
register_console for ttyS0. At that point the loop in register_console
tries to match it with the entries in the console_cmdline array.
Ideally this should match ttyS0 in entry 2, which is preferred, causing
it to be inserted first and to replace tty0 as CONSDEV. However, 8250
provides a "match" hook in its struct console, and that hook will match
"uart" as an alias to "ttyS". So we match uart0 at entry 0 in the array
which is not the preferred console and will not match entry 2 which is
since we break out of the loop on the first match. As a result,
we don't set CONSDEV and don't insert it first, but second in
the console list.
As a result, we end up with tty0 remaining first in the array, and thus
/dev/console going there instead of the last user specified one which
is ttyS0.
This tentative fix register_console() to scan first for consoles
specified on the command line, and only if none is found, to then
scan for consoles specified by the architecture.
Link: https://lore.kernel.org/r/20200213095133.23176-3-pmladek@suse.com
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Diffstat (limited to 'kernel/printk/console_cmdline.h')
-rw-r--r-- | kernel/printk/console_cmdline.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/printk/console_cmdline.h b/kernel/printk/console_cmdline.h index 11f19c466af5..3ca74ad391d6 100644 --- a/kernel/printk/console_cmdline.h +++ b/kernel/printk/console_cmdline.h @@ -6,6 +6,7 @@ struct console_cmdline { char name[16]; /* Name of the driver */ int index; /* Minor dev. to use */ + bool user_specified; /* Specified by command line vs. platform */ char *options; /* Options for the driver */ #ifdef CONFIG_A11Y_BRAILLE_CONSOLE char *brl_options; /* Options for braille driver */ |