Hei!
During weekend the linux-next was being broken by introducing a lockdep
warning in the console code
[ 0.000000] BIOS-e820: [mem 0x00000000e0000000-0x00000000ffffffff]
reserved
[ 0.000000]
[ 0.000000] =============================================
[ 0.000000] [ INFO: possible recursive locking detected ]
[ 0.000000] 3.15.0-rc2-next-20140428-00030-gd3550d8 #38 Not tainted
[ 0.000000] ---------------------------------------------
[ 0.000000] swapper/0 is trying to acquire lock:
[ 0.000000] (console_lock){......}, at: [<c10728cc>]
register_console+0x15e/0x295
[ 0.000000]
[ 0.000000] but task is already holding lock:
[ 0.000000] (console_lock){......}, at: [<c1071e7a>] vprintk_emit
+0x381/0x3ea
[ 0.000000]
[ 0.000000] other info that might help us debug this:
[ 0.000000] Possible unsafe locking scenario:
[ 0.000000]
[ 0.000000] CPU0
[ 0.000000] ----
[ 0.000000] lock(console_lock);
[ 0.000000] lock(console_lock);
[ 0.000000]
[ 0.000000] *** DEADLOCK ***
[ 0.000000]
[ 0.000000] May be due to missing lock nesting notation
[ 0.000000]
[ 0.000000] 3 locks held by swapper/0:
[ 0.000000] #0: (console_lock){......}, at: [<c1071e7a>]
vprintk_emit+0x381/0x3ea
[ 0.000000] #1: (console_lock){......}, at: [<c1071e7a>]
vprintk_emit+0x381/0x3ea
[ 0.000000] #2: (console_lock){......}, at: [<c1071e7a>]
vprintk_emit+0x381/0x3ea
[ 0.000000]
[ 0.000000] stack backtrace:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted
3.15.0-rc2-next-20140428-00030-gd3550d8 #38
[ 0.000000] 00000000 00000000 c186de1c c15878ae c1daf840 c186de88
c106c154 c1794d9d
[ 0.000000] c17958f7 c1794c9c 0000002a 00000000 00000000 c1daf840
c1983700 00000080
[ 0.000000] 04002001 c187a0b0 00000000 c1879ba0 c1879b40 c1879b40
00200046 00000000
[ 0.000000] Call Trace:
[ 0.000000] [<c15878ae>] dump_stack+0x49/0x73
[ 0.000000] [<c106c154>] __lock_acquire+0xb31/0xc7c
[ 0.000000] [<c106c33b>] lock_acquire+0x9c/0x111
[ 0.000000] [<c10728cc>] ? register_console+0x15e/0x295
[ 0.000000] [<c10707dd>] console_lock+0x41/0x46
[ 0.000000] [<c10728cc>] ? register_console+0x15e/0x295
[ 0.000000] [<c10728cc>] register_console+0x15e/0x295
[ 0.000000] [<c1582f80>] early_console_register+0x33/0x35
[ 0.000000] [<c1910411>] setup_early_printk+0x144/0x151
[ 0.000000] [<c19013f6>] do_early_param+0x41/0x73
[ 0.000000] [<c19013b5>] ? loglevel+0x2c/0x2c
[ 0.000000] [<c104c766>] parse_args+0x24f/0x307
[ 0.000000] [<c19013b5>] ? loglevel+0x2c/0x2c
[ 0.000000] [<c190169d>] parse_early_options+0x1c/0x21
[ 0.000000] [<c190169d>] ? parse_early_options+0x1c/0x21
[ 0.000000] [<c19013b5>] ? loglevel+0x2c/0x2c
[ 0.000000] [<c19016cc>] parse_early_param+0x2a/0x36
[ 0.000000] [<c19042c0>] setup_arch+0x3c9/0xc55
[ 0.000000] [<c1071ebe>] ? vprintk_emit+0x3c5/0x3ea
[ 0.000000] [<c1584869>] ? printk+0x28/0x2d
[ 0.000000] [<c1901754>] start_kernel+0x72/0x305
[ 0.000000] [<c19012b4>] i386_start_kernel+0x82/0x86
[ 0.000000] bootconsole [earlyhsu0] enabled
Bisecting shows the culprit (which I guessed before), namely commit
5dc90cb49691755faaad2a395d297d0162075eca ("printk: enable interrupts
before calling console_trylock_for_printk()").
Following patch helps me, but I'm not familiar with console locking
scheme, I believe there is a better solution.
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1700,8 +1700,10 @@ asmlinkage int vprintk_emit(int facility, int
level,
* The release will print out buffers and wake up /dev/kmsg and
syslog()
* users.
*/
+ lockdep_off();
if (console_trylock_for_printk())
console_unlock();
+ lockdep_on();
preempt_enable();
return printed_len;
--
Andy Shevchenko <andriy.shevche...@intel.com>
Intel Finland Oy
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