From b845b517b5e3706a3729f6ea83b88ab85f0725b0 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 8 Aug 2008 21:47:09 +0200 Subject: printk: robustify printk Avoid deadlocks against rq->lock and xtime_lock by deferring the klogd wakeup by polling from the timer tick. Signed-off-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- kernel/printk.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index b51b1567bb55..655cc2ca10cc 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -982,10 +982,25 @@ int is_console_locked(void) return console_locked; } -void wake_up_klogd(void) +static DEFINE_PER_CPU(int, printk_pending); + +void printk_tick(void) { - if (!oops_in_progress && waitqueue_active(&log_wait)) + if (__get_cpu_var(printk_pending)) { + __get_cpu_var(printk_pending) = 0; wake_up_interruptible(&log_wait); + } +} + +int printk_needs_cpu(int cpu) +{ + return per_cpu(printk_pending, cpu); +} + +void wake_up_klogd(void) +{ + if (waitqueue_active(&log_wait)) + __get_cpu_var(printk_pending) = 1; } /** -- cgit v1.2.1 From fa33507a22623b3bd543b15a21c362cf364b6cff Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 20 Aug 2008 09:31:26 +0200 Subject: printk: robustify printk, fix #2 Dmitry Adamushko reported: > [*] btw., with DEBUG being enabled, pr_debug() generates [1] when > debug_smp_processor_id() is used (CONFIG_DEBUG_PREEMPT). > > the problem seems to be caused by the following commit: > commit b845b517b5e3706a3729f6ea83b88ab85f0725b0 > Author: Peter Zijlstra > Date: Fri Aug 8 21:47:09 2008 +0200 > > printk: robustify printk > > > wake_up_klogd() -> __get_cpu_var() -> smp_processor_id() > > and that's being called from release_console_sem() which is, in turn, > said to be "may be called from any context" [2] > > and in this case, it seems to be called from some non-preemptible > context (although, it can't be printk()... > although, I haven't looked carefully yet). > > Provided [2], __get_cpu_var() is perhaps not the right solution there. > > > [1] > > [ 7697.942005] BUG: using smp_processor_id() in preemptible [00000000] code: syslogd/3542 > [ 7697.942005] caller is wake_up_klogd+0x1b/0x50 > [ 7697.942005] Pid: 3542, comm: syslogd Not tainted 2.6.27-rc3-tip-git #2 > [ 7697.942005] Call Trace: > [ 7697.942005] [] debug_smp_processor_id+0xe8/0xf0 > [ 7697.942005] [] wake_up_klogd+0x1b/0x50 > [ 7697.942005] [] release_console_sem+0x1e7/0x200 > [ 7697.942005] [] do_con_write+0xb7/0x1f30 > [ 7697.942005] [] ? show_trace+0x10/0x20 > [ 7697.942005] [] ? dump_stack+0x72/0x80 > [ 7697.942005] [] ? __ratelimit+0xbd/0xe0 > [ 7697.942005] [] ? debug_smp_processor_id+0xe8/0xf0 > [ 7697.942005] [] ? wake_up_klogd+0x1b/0x50 > [ 7697.942005] [] ? release_console_sem+0x1e7/0x200 > [ 7697.942005] [] con_write+0x19/0x30 > [ 7697.942005] [] write_chan+0x276/0x3c0 > [ 7697.942005] [] ? default_wake_function+0x0/0x10 > [ 7697.942005] [] ? _spin_lock_irqsave+0x22/0x50 > [ 7697.942005] [] tty_write+0x194/0x260 > [ 7697.942005] [] ? write_chan+0x0/0x3c0 > [ 7697.942005] [] redirected_tty_write+0xa4/0xb0 > [ 7697.942005] [] ? redirected_tty_write+0x0/0xb0 > [ 7697.942005] [] do_loop_readv_writev+0x52/0x80 > [ 7697.942005] [] do_readv_writev+0x1bd/0x1d0 > [ 7697.942005] [] vfs_writev+0x39/0x60 > [ 7697.942005] [] sys_writev+0x50/0x90 > [ 7697.942005] [] system_call_fastpath+0x16/0x1b Signed-off-by: Peter Zijlstra Reported-by: Dmitry Adamushko Signed-off-by: Ingo Molnar --- kernel/printk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index 655cc2ca10cc..57e9cd7a9581 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -1000,7 +1000,7 @@ int printk_needs_cpu(int cpu) void wake_up_klogd(void) { if (waitqueue_active(&log_wait)) - __get_cpu_var(printk_pending) = 1; + __raw_get_cpu_var(printk_pending) = 1; } /** -- cgit v1.2.1 From 1fa63a817d27af7dc0d5ed454eb8fe5dec65fac7 Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Wed, 20 Aug 2008 14:40:55 +0200 Subject: printk: robustify printk, update comment Remove the comment describing the possibility of printk() deadlocking on runqueue lock. Signed-off-by: Jiri Kosina Acked-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- kernel/printk.c | 3 --- 1 file changed, 3 deletions(-) (limited to 'kernel/printk.c') diff --git a/kernel/printk.c b/kernel/printk.c index 57e9cd7a9581..6f27c6a4bdc9 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -577,9 +577,6 @@ static int have_callable_console(void) * @fmt: format string * * This is printk(). It can be called from any context. We want it to work. - * Be aware of the fact that if oops_in_progress is not set, we might try to - * wake klogd up which could deadlock on runqueue lock if printk() is called - * from scheduler code. * * We try to grab the console_sem. If we succeed, it's easy - we log the output and * call the console drivers. If we fail to get the semaphore we place the output -- cgit v1.2.1