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authorJane Li <jiel@marvell.com>2014-04-03 14:48:45 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-04-03 16:21:08 -0700
commit72581487a61f6304a7cc32e189eb65fb1c920a53 (patch)
tree982c7f07bf2315fcf9b7d14eef1640c748ffb025 /kernel
parentd487d57581057abd271651334ea2996aa1b31e28 (diff)
downloadlinux-72581487a61f6304a7cc32e189eb65fb1c920a53.tar.gz
printk: fix one circular lockdep warning about console_lock
Fix a warning about possible circular locking dependency. If do in following sequence: enter suspend -> resume -> plug-out CPUx (echo 0 > cpux/online) lockdep will show warning as following: ====================================================== [ INFO: possible circular locking dependency detected ] 3.10.0 #2 Tainted: G O ------------------------------------------------------- sh/1271 is trying to acquire lock: (console_lock){+.+.+.}, at: console_cpu_notify+0x20/0x2c but task is already holding lock: (cpu_hotplug.lock){+.+.+.}, at: cpu_hotplug_begin+0x2c/0x58 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (cpu_hotplug.lock){+.+.+.}: lock_acquire+0x98/0x12c mutex_lock_nested+0x50/0x3d8 cpu_hotplug_begin+0x2c/0x58 _cpu_up+0x24/0x154 cpu_up+0x64/0x84 smp_init+0x9c/0xd4 kernel_init_freeable+0x78/0x1c8 kernel_init+0x8/0xe4 ret_from_fork+0x14/0x2c -> #1 (cpu_add_remove_lock){+.+.+.}: lock_acquire+0x98/0x12c mutex_lock_nested+0x50/0x3d8 disable_nonboot_cpus+0x8/0xe8 suspend_devices_and_enter+0x214/0x448 pm_suspend+0x1e4/0x284 try_to_suspend+0xa4/0xbc process_one_work+0x1c4/0x4fc worker_thread+0x138/0x37c kthread+0xa4/0xb0 ret_from_fork+0x14/0x2c -> #0 (console_lock){+.+.+.}: __lock_acquire+0x1b38/0x1b80 lock_acquire+0x98/0x12c console_lock+0x54/0x68 console_cpu_notify+0x20/0x2c notifier_call_chain+0x44/0x84 __cpu_notify+0x2c/0x48 cpu_notify_nofail+0x8/0x14 _cpu_down+0xf4/0x258 cpu_down+0x24/0x40 store_online+0x30/0x74 dev_attr_store+0x18/0x24 sysfs_write_file+0x16c/0x19c vfs_write+0xb4/0x190 SyS_write+0x3c/0x70 ret_fast_syscall+0x0/0x48 Chain exists of: console_lock --> cpu_add_remove_lock --> cpu_hotplug.lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(cpu_hotplug.lock); lock(cpu_add_remove_lock); lock(cpu_hotplug.lock); lock(console_lock); *** DEADLOCK *** There are three locks involved in two sequence: a) pm suspend: console_lock (@suspend_console()) cpu_add_remove_lock (@disable_nonboot_cpus()) cpu_hotplug.lock (@_cpu_down()) b) Plug-out CPUx: cpu_add_remove_lock (@(cpu_down()) cpu_hotplug.lock (@_cpu_down()) console_lock (@console_cpu_notify()) => Lockdeps prints warning log. There should be not real deadlock, as flag of console_suspended can protect this. Although console_suspend() releases console_sem, it doesn't tell lockdep about it. That results in the lockdep warning about circular locking when doing the following: enter suspend -> resume -> plug-out CPUx (echo 0 > cpux/online) Fix the problem by telling lockdep we actually released the semaphore in console_suspend() and acquired it again in console_resume(). Signed-off-by: Jane Li <jiel@marvell.com> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/printk/printk.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ff9faf4e3cd..a45b5096229 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1883,6 +1883,7 @@ void suspend_console(void)
console_lock();
console_suspended = 1;
up(&console_sem);
+ mutex_release(&console_lock_dep_map, 1, _RET_IP_);
}
void resume_console(void)
@@ -1890,6 +1891,7 @@ void resume_console(void)
if (!console_suspend_enabled)
return;
down(&console_sem);
+ mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);
console_suspended = 0;
console_unlock();
}