linux-stable.git/kernel/printk/printk.c, branch linux-4.9.y

printk: fix return value of printk.devkmsg __setup handler

2022-04-20T07:06:33+00:00

[ Upstream commit b665eae7a788c5e2bc10f9ac3c0137aa0ad1fc97 ]

If an invalid option value is used with "printk.devkmsg=",
it is silently ignored.
If a valid option value is used, it is honored but the wrong return
value (0) is used, indicating that the command line option had an
error and was not handled. This string is not added to init's
environment strings due to init/main.c::unknown_bootoption()
checking for a '.' in the boot option string and then considering
that string to be an "Unused module parameter".

Print a warning message if a bad option string is used.
Always return 1 from the __setup handler to indicate that the command
line option has been handled.

Fixes: 750afe7babd1 ("printk: add kernel parameter to control writes to /dev/kmsg")
Signed-off-by: Randy Dunlap 
Reported-by: Igor Zhbanov 
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Cc: Borislav Petkov 
Cc: Andrew Morton 
Cc: Petr Mladek 
Cc: Sergey Senozhatsky 
Cc: Steven Rostedt 
Cc: John Ogness 
Reviewed-by: John Ogness 
Reviewed-by: Sergey Senozhatsky 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20220228220556.23484-1-rdunlap@infradead.org
Signed-off-by: Sasha Levin

printk/console: Allow to disable console output by using console="" or console=null

2021-11-12T12:18:02+00:00

commit 3cffa06aeef7ece30f6b5ac0ea51f264e8fea4d0 upstream.

The commit 48021f98130880dd74 ("printk: handle blank console arguments
passed in.") prevented crash caused by empty console= parameter value.

Unfortunately, this value is widely used on Chromebooks to disable
the console output. The above commit caused performance regression
because the messages were pushed on slow console even though nobody
was watching it.

Use ttynull driver explicitly for console="" and console=null
parameters. It has been created for exactly this purpose.

It causes that preferred_console is set. As a result, ttySX and ttyX
are not used as a fallback. And only ttynull console gets registered by
default.

It still allows to register other consoles either by additional console=
parameters or SPCR. It prevents regression because it worked this way even
before. Also it is a sane semantic. Preventing output on all consoles
should be done another way, for example, by introducing mute_console
parameter.

Link: https://lore.kernel.org/r/20201006025935.GA597@jagdpanzerIV.localdomain
Suggested-by: Sergey Senozhatsky 
Reviewed-by: Guenter Roeck 
Tested-by: Guenter Roeck 
Acked-by: Sergey Senozhatsky 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20201111135450.11214-3-pmladek@suse.com
Cc: Yi Fan 
Signed-off-by: Greg Kroah-Hartman

printk: handle blank console arguments passed in.

2020-10-01T18:40:14+00:00

[ Upstream commit 48021f98130880dd74286459a1ef48b5e9bc374f ]

If uboot passes a blank string to console_setup then it results in
a trashed memory. Ultimately, the kernel crashes during freeing up
the memory.

This fix checks if there is a blank parameter being
passed to console_setup from uboot. In case it detects that
the console parameter is blank then it doesn't setup the serial
device and it gracefully exits.

Link: https://lore.kernel.org/r/20200522065306.83-1-shreyas.joshi@biamp.com
Signed-off-by: Shreyas Joshi 
Acked-by: Sergey Senozhatsky 
[pmladek@suse.com: Better format the commit message and code, remove unnecessary brackets.]
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin

printk: fix integer overflow in setup_log_buf()

2019-11-28T17:28:15+00:00

[ Upstream commit d2130e82e9454304e9b91ba9da551b5989af8c27 ]

The way we calculate logbuf free space percentage overflows signed
integer:

	int free;

	free = __LOG_BUF_LEN - log_next_idx;
	pr_info("early log buf free: %u(%u%%)\n",
		free, (free * 100) / __LOG_BUF_LEN);

We support LOG_BUF_LEN of up to 1<<25 bytes. Since setup_log_buf() is
called during early init, logbuf is mostly empty, so

	__LOG_BUF_LEN - log_next_idx

is close to 1<<25. Thus when we multiply it by 100, we overflow signed
integer value range: 100 is 2^6 + 2^5 + 2^2.

Example, booting with LOG_BUF_LEN 1<<25 and log_buf_len=2G
boot param:

[    0.075317] log_buf_len: -2147483648 bytes
[    0.075319] early log buf free: 33549896(-28%)

Make "free" unsigned integer and use appropriate printk() specifier.

Link: http://lkml.kernel.org/r/20181010113308.9337-1-sergey.senozhatsky@gmail.com
To: Steven Rostedt 
Cc: linux-kernel@vger.kernel.org
Cc: Sergey Senozhatsky 
Signed-off-by: Sergey Senozhatsky 
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin

printk: Give error on attempt to set log buffer length to over 2G

2019-11-25T08:53:45+00:00

[ Upstream commit e6fe3e5b7d16e8f146a4ae7fe481bc6e97acde1e ]

The current printk() is ready to handle log buffer size up to 2G.
Give an explicit error for users who want to use larger log buffer.

Also fix printk formatting to show the 2G as a positive number.

Link: http://lkml.kernel.org/r/20181008135916.gg4kkmoki5bgtco5@pathway.suse.cz
Cc: rostedt@goodmis.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Sergey Senozhatsky 
Signed-off-by: He Zhe 
Reviewed-by: Sergey Senozhatsky 
[pmladek: Fixed to the really safe limit 2GB.]
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin

printk: Do not lose last line in kmsg buffer dump

2019-10-05T10:30:31+00:00

[ Upstream commit b46eff55ad5bd98e746c0a7022fe7ee071de5fee ]

kmsg_dump_get_buffer() is supposed to select all the youngest log
messages which fit into the provided buffer.  It determines the correct
start index by using msg_print_text() with a NULL buffer to calculate
the size of each entry.  However, when performing the actual writes,
msg_print_text() only writes the entry to the buffer if the written len
is lesser than the size of the buffer.  So if the lengths of the
selected youngest log messages happen to precisely fill up the provided
buffer, the last log message is not included.

We don't want to modify msg_print_text() to fill up the buffer and start
returning a length which is equal to the size of the buffer, since
callers of its other users, such as kmsg_dump_get_line(), depend upon
the current behaviour.

Instead, fix kmsg_dump_get_buffer() to compensate for this.

For example, with the following two final prints:

[    6.427502] AAAAAAAAAAAAA
[    6.427769] BBBBBBBB12345

A dump of a 64-byte buffer filled by kmsg_dump_get_buffer(), before this
patch:

 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 35 32 32 31 39 37  <0>[    6.522197
 00000010: 5d 20 41 41 41 41 41 41 41 41 41 41 41 41 41 0a  ] AAAAAAAAAAAAA.
 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................

After this patch:

 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 34 35 36 36 37 38  <0>[    6.456678
 00000010: 5d 20 42 42 42 42 42 42 42 42 31 32 33 34 35 0a  ] BBBBBBBB12345.
 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................

Link: http://lkml.kernel.org/r/20190711142937.4083-1-vincent.whitchurch@axis.com
Fixes: e2ae715d66bf4bec ("kmsg - kmsg_dump() use iterator to receive log buffer content")
To: rostedt@goodmis.org
Cc: linux-kernel@vger.kernel.org
Cc:  # v3.5+
Signed-off-by: Vincent Whitchurch 
Reviewed-by: Sergey Senozhatsky 
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin

printk: remove games with previous record flags

2019-10-05T10:30:30+00:00

[ Upstream commit 5aa068ea4082b39eafc356c27c9ecd155b0895f6 ]

The record logging code looks at the previous record flags in various
ways, and they are all wrong.

You can't use the previous record flags to determine anything about the
next record, because they may simply not be related.  In particular, the
reason the previous record was a continuation record may well be exactly
_because_ the new record was printed by a different process, which is
why the previous record was flushed.

So all those games are simply wrong, and make the code hard to
understand (because the code fundamentally cdoes not make sense).

So remove it.

Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin

printk: Fix panic caused by passing log_buf_len to command line

2018-11-13T19:17:01+00:00

commit 277fcdb2cfee38ccdbe07e705dbd4896ba0c9930 upstream.

log_buf_len_setup does not check input argument before passing it to
simple_strtoull. The argument would be a NULL pointer if "log_buf_len",
without its value, is set in command line and thus causes the following
panic.

PANIC: early exception 0xe3 IP 10:ffffffffaaeacd0d error 0 cr2 0x0
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc4-yocto-standard+ #1
[    0.000000] RIP: 0010:_parse_integer_fixup_radix+0xd/0x70
...
[    0.000000] Call Trace:
[    0.000000]  simple_strtoull+0x29/0x70
[    0.000000]  memparse+0x26/0x90
[    0.000000]  log_buf_len_setup+0x17/0x22
[    0.000000]  do_early_param+0x57/0x8e
[    0.000000]  parse_args+0x208/0x320
[    0.000000]  ? rdinit_setup+0x30/0x30
[    0.000000]  parse_early_options+0x29/0x2d
[    0.000000]  ? rdinit_setup+0x30/0x30
[    0.000000]  parse_early_param+0x36/0x4d
[    0.000000]  setup_arch+0x336/0x99e
[    0.000000]  start_kernel+0x6f/0x4ee
[    0.000000]  x86_64_start_reservations+0x24/0x26
[    0.000000]  x86_64_start_kernel+0x6f/0x72
[    0.000000]  secondary_startup_64+0xa4/0xb0

This patch adds a check to prevent the panic.

Link: http://lkml.kernel.org/r/1538239553-81805-1-git-send-email-zhe.he@windriver.com
Cc: stable@vger.kernel.org
Cc: rostedt@goodmis.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: He Zhe 
Reviewed-by: Sergey Senozhatsky 
Signed-off-by: Petr Mladek 
Signed-off-by: Greg Kroah-Hartman

printk: Correctly handle preemption in console_unlock()

2018-03-22T08:17:47+00:00

[ Upstream commit 257ab443118bffc7fdcef38f49cf59be68a3e362 ]

Some console drivers code calls console_conditional_schedule()
that looks at @console_may_schedule. The value must be cleared
when the drivers are called from console_unlock() with
interrupts disabled. But rescheduling is fine when the same
code is called, for example, from tty operations where the
console semaphore is taken via console_lock().

This is why @console_may_schedule is cleared before calling console
drivers. The original value is stored to decide if we could sleep
between lines.

Now, @console_may_schedule is not cleared when we call
console_trylock() and jump back to the "again" goto label.
This has become a problem, since the commit 6b97a20d3a7909daa066
("printk: set may_schedule for some of console_trylock() callers").
@console_may_schedule might get enabled now.

There is also the opposite problem. console_lock() can be called
only from preemptive context. It can always enable scheduling in
the console code. But console_trylock() is not able to detect it
when CONFIG_PREEMPT_COUNT is disabled. Therefore we should use the
original @console_may_schedule value after re-acquiring
the console semaphore in console_unlock().

This patch solves both problems by moving the "again" goto label.

Alternative solution was to clear and restore the value around
call_console_drivers(). Then console_conditional_schedule() could
be used also inside console_unlock(). But there was a potential race
with console_flush_on_panic() as reported by Sergey Senozhatsky.
That function should be called only where there is only one CPU
and with interrupts disabled. But better be on the safe side
because stopping CPUs might fail.

Fixes: 6b97a20d3a7909 ("printk: set may_schedule for some of console_trylock() callers")
Link: http://lkml.kernel.org/r/1490372045-22288-1-git-send-email-pmladek@suse.com
Suggested-by: Tetsuo Handa 
Cc: Steven Rostedt 
Cc: Peter Zijlstra 
Cc: Andrew Morton 
Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: linux-fbdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Sergey Senozhatsky 
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

printk: use rcuidle console tracepoint

2017-02-23T16:44:36+00:00

commit fc98c3c8c9dcafd67adcce69e6ce3191d5306c9c upstream.

Use rcuidle console tracepoint because, apparently, it may be issued
from an idle CPU:

  hw-breakpoint: Failed to enable monitor mode on CPU 0.
  hw-breakpoint: CPU 0 failed to disable vector catch

  ===============================
  [ ERR: suspicious RCU usage.  ]
  4.10.0-rc8-next-20170215+ #119 Not tainted
  -------------------------------
  ./include/trace/events/printk.h:32 suspicious rcu_dereference_check() usage!

  other info that might help us debug this:

  RCU used illegally from idle CPU!
  rcu_scheduler_active = 2, debug_locks = 0
  RCU used illegally from extended quiescent state!
  2 locks held by swapper/0/0:
   #0:  (cpu_pm_notifier_lock){......}, at: [] cpu_pm_exit+0x10/0x54
   #1:  (console_lock){+.+.+.}, at: [] vprintk_emit+0x264/0x474

  stack backtrace:
  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.10.0-rc8-next-20170215+ #119
  Hardware name: Generic OMAP4 (Flattened Device Tree)
    console_unlock
    vprintk_emit
    vprintk_default
    printk
    reset_ctrl_regs
    dbg_cpu_pm_notify
    notifier_call_chain
    cpu_pm_exit
    omap_enter_idle_coupled
    cpuidle_enter_state
    cpuidle_enter_state_coupled
    do_idle
    cpu_startup_entry
    start_kernel

This RCU warning, however, is suppressed by lockdep_off() in printk().
lockdep_off() increments the ->lockdep_recursion counter and thus
disables RCU_LOCKDEP_WARN() and debug_lockdep_rcu_enabled(), which want
lockdep to be enabled "current->lockdep_recursion == 0".

Link: http://lkml.kernel.org/r/20170217015932.11898-1-sergey.senozhatsky@gmail.com
Signed-off-by: Sergey Senozhatsky 
Reported-by: Tony Lindgren 
Tested-by: Tony Lindgren 
Acked-by: Paul E. McKenney 
Acked-by: Steven Rostedt (VMware) 
Cc: Petr Mladek 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Tony Lindgren 
Cc: Russell King 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman