Message-ID: <20080226225242.GA15926@redhat.com>
Date:	Tue, 26 Feb 2008 17:52:43 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [patch 1/7] Immediate Values - Architecture Independent Code

On Sat, Feb 02, 2008 at 04:08:29PM -0500, Mathieu Desnoyers wrote:
> Changelog:
> 
> - section __imv is already SHF_ALLOC
> - Because of the wonders of ELF, section 0 has sh_addr and sh_size 0.  So
>   the if (immediateindex) is unnecessary here.
> - Remove module_mutex usage: depend on functions implemented in module.c for
>   that.

hi,

In testing this patch, i've run across a deadlock...apply_imv_update() can get
called again before, ipi_busy_loop() has had a chance to finsh, and set 
wait_sync back to its initial value. This causes ipi_busy_loop() to get stuck
indefinitely and the subsequent apply_imv_update() hangs. I've shown this 
deadlock below using nmi_watchdog=1 in item 1). 

After hitting this deadlock i modified apply_imv_update() to wait for 
ipi_busy_loop(), to finish, however this resulted in a 3 way deadlock. Process
A held a read lock on tasklist_lock, then process B called apply_imv_update().
Process A received the IPI and begins executing ipi_busy_loop(). Then process
C takes a write lock irq on the task list lock, before receiving the IPI. Thus,
process A holds up process C, and C can't get an IPI b/c interrupts are
disabled. i believe this is an inherent problem in using smp_call_function, in
that one can't synchronize the processes on each other...you can reproduce
these issues using the test module below item 2)

In order to address these issues, i've modified stop_machine_run() to take an
new third parameter, RUN_ALL, to allow stop_machine_run() to run a function
on all cpus, item 3). I then modified kernel/immediate.c to use this new 
infrastructure item 4). the code in immediate.c simplifies quite a bit. This
new code has been robust through all testing thus far.

thanks,

-Jason

1)

 NMI Watchdog detected LOCKUP on CPU 3
CPU 3
Modules linked in: toggle_tester ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 xt_state nf]Pid: 0, comm: swapper Not tainted 2.6.24-git12markers #1
RIP: 0010:[<ffffffff8106e7cc>]  [<ffffffff8106e7cc>] ipi_busy_loop+0x19/0x41
RSP: 0018:ffff81007fbdff70  EFLAGS: 00000002
RAX: 0000000000000006 RBX: 0000000000000000 RCX: ffff81007fbd2930
RDX: ffffffff81491b80 RSI: 0000000000000046 RDI: 0000000000000000
RBP: ffff81007fbdff78 R08: ffff81007fbdff78 R09: ffff81007dd91e80
R10: ffff810001030b80 R11: 0000000000000246 R12: ffffffff8106e7b3
R13: 0000000000000000 R14: ffffffff81491a80 R15: ffff810001030a80
FS:  0000000000000000(0000) GS:ffff81007f801c80(0000) knlGS:0000000000000000
CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
CR2: 00000000025e8d68 CR3: 000000007549c000 CR4: 00000000000026e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process swapper (pid: 0, threadinfo ffff81007fbd6000, task ffff81007fbd2930)
Stack:  0000000000000000 ffff81007fbdffa8 ffffffff8101ca4e ffff81007fbdffa8
 ffffffff8100b0e2 0000000000000003 0000000000000040 ffff81007fbd7e60
 ffffffff8100cac6 ffff81007fbd7e60 <EOI>  ffff81007fbd7ee8 0000000000000246
Call Trace:
 <IRQ>  [<ffffffff8101ca4e>] smp_call_function_interrupt+0x48/0x71
 [<ffffffff8100b0e2>] ? mwait_idle+0x0/0x4a
 [<ffffffff8100cac6>] call_function_interrupt+0x66/0x70
 <EOI>  [<ffffffff8100b127>] ? mwait_idle+0x45/0x4a
 [<ffffffff8100a723>] ? enter_idle+0x22/0x24
 [<ffffffff8100b06f>] ? cpu_idle+0x97/0xc1
 [<ffffffff81270a35>] ? start_secondary+0x3ba/0x3c6


---[ end trace 738433437d960ebc ]---
NMI Watchdog detected LOCKUP on CPU 2
CPU 2
Modules linked in: toggle_tester ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 xt_state nf]Pid: 9704, comm: toggle-writer Not tainted 2.6.24-git12markers #1
RIP: 0010:[<ffffffff8101c717>]  [<ffffffff8101c717>] __smp_call_function_mask+0x9f/0xc1
RSP: 0018:ffff81003ac35da8  EFLAGS: 00000297
RAX: 00000000000008fc RBX: 000000000000000b RCX: 00000000000008fc
RDX: 00000000000008fc RSI: 00000000000000fc RDI: 000000000000000b
RBP: ffff81003ac35e08 R08: ffffffff8840504f R09: 00007f01f07696f0
R10: 0000000000000022 R11: 0000000000000246 R12: 0000000000000003
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff8106e7b3
FS:  00007f01f07696f0(0000) GS:ffff81007f801980(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007f01f0796000 CR3: 000000006bcdf000 CR4: 00000000000026e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process toggle-writer (pid: 9704, threadinfo ffff81003ac34000, task ffff81003ad14930)
Stack:  ffffffff8106e7b3 0000000000000000 0000000000000002 00003fff00000000
 000000000000000b ffffffff81075c03 00000010001280d2 0000000000000000
 0000000000000000 ffffffff8106e7b3 000000000000000f 0000000000000005
Call Trace:
 [<ffffffff8106e7b3>] ? ipi_busy_loop+0x0/0x41
 [<ffffffff81075c03>] ? __alloc_pages+0x8e/0x337
 [<ffffffff8106e7b3>] ? ipi_busy_loop+0x0/0x41
 [<ffffffff8101c783>] smp_call_function_mask+0x4a/0x59
 [<ffffffff8101c7ab>] smp_call_function+0x19/0x1b
 [<ffffffff8106e703>] imv_update_range+0xd7/0x16e
 [<ffffffff8105494e>] _module_imv_update+0x35/0x54
 [<ffffffff81054982>] module_imv_update+0x15/0x23
 [<ffffffff884050c4>] :toggle_tester:proc_toggle_write+0x4c/0x64
 [<ffffffff810d64a4>] proc_reg_write+0x7b/0x96
 [<ffffffff81099f72>] vfs_write+0xae/0x157
 [<ffffffff8109a53f>] sys_write+0x47/0x70
 [<ffffffff8100c0e9>] tracesys+0xdc/0xe1

Code: f8 48 3b 5d c0 48 8b 05 28 1a 41 00 75 0a bf fc 00 00 00 ff 50 38 eb 0f be fc 00 00 00 48
---[ end trace 738433437d960ebc ]---
NMI Watchdog detected LOCKUP on CPU 1
CPU 1
Modules linked in: toggle_tester ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 xt_state nf]Pid: 0, comm: swapper Not tainted 2.6.24-git12markers #1
RIP: 0010:[<ffffffff8106e7cc>]  [<ffffffff8106e7cc>] ipi_busy_loop+0x19/0x41
RSP: 0018:ffff81007fb6ff70  EFLAGS: 00000002
RAX: 0000000000000006 RBX: 0000000000000000 RCX: ffff81007fb5f260
RDX: ffffffff81491b80 RSI: 0000000000000046 RDI: 0000000000000000
RBP: ffff81007fb6ff78 R08: ffff81007fb6ff78 R09: ffff810001016700
R10: ffff810001018b80 R11: 0000000000000001 R12: ffffffff8106e7b3
R13: 0000000000000000 R14: ffffffff81491a80 R15: ffff810001018a80
FS:  0000000000000000(0000) GS:ffff81007f801680(0000) knlGS:0000000000000000
CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
CR2: 00000031fac9ac20 CR3: 00000000778e6000 CR4: 00000000000026e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process swapper (pid: 0, threadinfo ffff81007fb6a000, task ffff81007fb5f260)
Stack:  0000000000000000 ffff81007fb6ffa8 ffffffff8101ca4e ffff81007fb6ffa8
 ffffffff8100b0e2 0000000000000001 0000000000000040 ffff81007fb6be60
 ffffffff8100cac6 ffff81007fb6be60 <EOI>  ffff81007fb6bee8 0000000000000001
Call Trace:
 <IRQ>  [<ffffffff8101ca4e>] smp_call_function_interrupt+0x48/0x71
 [<ffffffff8100b0e2>] ? mwait_idle+0x0/0x4a
 [<ffffffff8100cac6>] call_function_interrupt+0x66/0x70
 <EOI>  [<ffffffff8100b127>] ? mwait_idle+0x45/0x4a
 [<ffffffff8100a723>] ? enter_idle+0x22/0x24
 [<ffffffff8100b06f>] ? cpu_idle+0x97/0xc1
 [<ffffffff81270a35>] ? start_secondary+0x3ba/0x3c6

Code: 81 48 c7 c7 02 fd 36 81 48 89 e5 e8 7b fe ff ff c9 c3 55 48 89 e5 53 9c 5e fa f0 ff 0d 82
---[ end trace 738433437d960ebc ]---
NMI Watchdog detected LOCKUP on CPU 0
Kernel panic - not syncing: Aiee, killing interrupt handler!
CPU 0
Modules linked in: toggle_tester ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 xt_state nf]Pid: 0, comm: swapper Not tainted 2.6.24-git12markers #1
RIP: 0010:[<ffffffff8106e7e6>]  [<ffffffff8106e7e6>] ipi_busy_loop+0x33/0x41
RSP: 0018:ffffffff81498f70  EFLAGS: 00000006
RAX: 0000000000000004 RBX: 0000000000000000 RCX: ffffffff81394620
RDX: ffffffff81491b80 RSI: 0000000000000046 RDI: 0000000000000000
RBP: ffffffff81498f78 R08: ffffffff81498f78 R09: ffff810062cc1e98
R10: ffff81000100cb80 R11: ffff810062cc1d58 R12: ffffffff8106e7b3
R13: 0000000000000000 R14: ffffffff81466640 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffffffff813d2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
CR2: 00000031fac6f060 CR3: 0000000000201000 CR4: 00000000000026e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process swapper (pid: 0, threadinfo ffffffff81434000, task ffffffff81394620)
Stack:  0000000000000000 ffffffff81498fa8 ffffffff8101ca4e ffffffff8100b0e2
 ffffffff8100b0e2 0000000000000000 ffffffffffffffff ffffffff81435ec0
 ffffffff8100cac6 ffffffff81435ec0 <EOI>  ffffffff81435f48 ffff810062cc1d58
Call Trace:
 <IRQ>  [<ffffffff8101ca4e>] smp_call_function_interrupt+0x48/0x71
 [<ffffffff8100b0e2>] ? mwait_idle+0x0/0x4a
 [<ffffffff8100b0e2>] ? mwait_idle+0x0/0x4a
 [<ffffffff8100cac6>] call_function_interrupt+0x66/0x70
 <EOI>  [<ffffffff8100b127>] ? mwait_idle+0x45/0x4a
 [<ffffffff8100a723>] ? enter_idle+0x22/0x24
 [<ffffffff8100b06f>] ? cpu_idle+0x97/0xc1
 [<ffffffff81266ee6>] ? rest_init+0x5a/0x5c

Code: f0 ff 0d 82 6b 49 00 0f ae f0 48 63 05 78 6b 49 00 48 3b 05 5d 6b 49 00 7f ed f0 ff 0d 68
---[ end trace 738433437d960ebc ]---


2)


--- /dev/null
+++ b/samples/markers/toggle-tester.c
@@ -0,0 +1,90 @@
+/* probe-example.c
+ *
+ * toggle module to test immedidate infrastructure.
+ *
+ * (C) Copyright 2007 Jason Baron <jbaron@...hat.com>
+ *
+ * This file is released under the GPLv2.
+ * See the file COPYING for more details.
+ */
+
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/marker.h>
+#include <asm/atomic.h>
+#include <linux/seq_file.h>
+#include <linux/fs.h>
+#include <linux/proc_fs.h>
+
+static DECLARE_MUTEX(toggle_mutex);
+DEFINE_IMV(char, toggle_value) = 0;
+
+static ssize_t proc_toggle_write(struct file *file, const char __user *buf,
+                                size_t length, loff_t *ppos)
+{
+	int i;
+
+	down(&toggle_mutex);
+	i = imv_read(toggle_value);
+	imv_set(toggle_value, !i);
+	up(&toggle_mutex);
+
+	return 0;
+}
+
+static int proc_toggle_show(struct seq_file *s, void *p)
+{
+	int i;
+
+	down(&toggle_mutex);        
+        i = imv_read(toggle_value);
+	up(&toggle_mutex);
+
+	seq_printf(s, "%u\n", i);
+
+        return 0;
+}
+
+
+static int proc_toggle_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, proc_toggle_show, NULL);
+}
+
+
+static const struct file_operations toggle_operations = {
+	.open           = proc_toggle_open,
+	.read           = seq_read,
+	.write          = proc_toggle_write,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+	
+
+struct proc_dir_entry *pde;
+
+static int __init toggle_init(void)
+{
+	
+	pde = create_proc_entry("toggle", 0, NULL);
+	if (!pde)
+		return -ENOMEM;
+	pde->proc_fops = &toggle_operations;
+
+
+	return 0;
+}
+
+static void __exit toggle_fini(void)
+{
+	remove_proc_entry("toggle", &proc_root);
+	
+}
+
+module_init(toggle_init);
+module_exit(toggle_fini);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jason Baron");
+MODULE_DESCRIPTION("testing immediate implementation");


3)


diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 5bfc553..1ab1c5b 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -8,6 +8,9 @@
 #include <asm/system.h>
 
 #if defined(CONFIG_STOP_MACHINE) && defined(CONFIG_SMP)
+
+#define RUN_ALL ~0U
+
 /**
  * stop_machine_run: freeze the machine on all CPUs and run this function
  * @fn: the function to run
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 51b5ee5..e6ee46f 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -23,9 +23,17 @@ enum stopmachine_state {
 	STOPMACHINE_WAIT,
 	STOPMACHINE_PREPARE,
 	STOPMACHINE_DISABLE_IRQ,
+	STOPMACHINE_RUN,
 	STOPMACHINE_EXIT,
 };
 
+struct stop_machine_data {
+	int (*fn)(void *);
+	void *data;
+	struct completion done;
+	int run_all;
+} smdata;
+
 static enum stopmachine_state stopmachine_state;
 static unsigned int stopmachine_num_threads;
 static atomic_t stopmachine_thread_ack;
@@ -35,6 +43,7 @@ static int stopmachine(void *cpu)
 {
 	int irqs_disabled = 0;
 	int prepared = 0;
+	int ran = 0;
 
 	set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
 
@@ -59,6 +68,11 @@ static int stopmachine(void *cpu)
 			prepared = 1;
 			smp_mb(); /* Must read state first. */
 			atomic_inc(&stopmachine_thread_ack);
+		} else if (stopmachine_state == STOPMACHINE_RUN && !ran) {
+			smdata.fn(smdata.data);
+			ran = 1;
+			smp_mb(); /* Must read state first. */
+			atomic_inc(&stopmachine_thread_ack);
 		}
 		/* Yield in first stage: migration threads need to
 		 * help our sisters onto their CPUs. */
@@ -136,12 +150,10 @@ static void restart_machine(void)
 	preempt_enable_no_resched();
 }
 
-struct stop_machine_data
+static void run_other_cpus(void)
 {
-	int (*fn)(void *);
-	void *data;
-	struct completion done;
-};
+	stopmachine_set_state(STOPMACHINE_RUN);
+}
 
 static int do_stop(void *_smdata)
 {
@@ -151,6 +163,8 @@ static int do_stop(void *_smdata)
 	ret = stop_machine();
 	if (ret == 0) {
 		ret = smdata->fn(smdata->data);
+		if (smdata->run_all)
+			run_other_cpus();
 		restart_machine();
 	}
 
@@ -170,17 +184,16 @@ static int do_stop(void *_smdata)
 struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
 				       unsigned int cpu)
 {
-	struct stop_machine_data smdata;
 	struct task_struct *p;
 
+	down(&stopmachine_mutex);
 	smdata.fn = fn;
 	smdata.data = data;
+	smdata.run_all = (cpu == RUN_ALL) ? 1 : 0;
 	init_completion(&smdata.done);
-
-	down(&stopmachine_mutex);
-
+	smp_wmb();
 	/* If they don't care which CPU fn runs on, bind to any online one. */
-	if (cpu == NR_CPUS)
+	if (cpu == NR_CPUS || cpu == RUN_ALL)
 		cpu = raw_smp_processor_id();
 
 	p = kthread_create(do_stop, &smdata, "kstopmachine");


4)


diff --git a/kernel/immediate.c b/kernel/immediate.c
index 4c36a89..39ec13e 100644
--- a/kernel/immediate.c
+++ b/kernel/immediate.c
@@ -20,6 +20,7 @@
 #include <linux/immediate.h>
 #include <linux/memory.h>
 #include <linux/cpu.h>
+#include <linux/stop_machine.h>
 
 #include <asm/cacheflush.h>
 
@@ -30,6 +31,23 @@ static int imv_early_boot_complete;
 
 extern const struct __imv __start___imv[];
 extern const struct __imv __stop___imv[];
+int started;
+
+int stop_machine_imv_update(void *imv_ptr)
+{
+	struct __imv *imv = imv_ptr;
+
+	if (!started) {
+		text_poke((void *)imv->imv, (void *)imv->var, imv->size);
+		started = 1;
+		smp_wmb();
+	} else
+		sync_core();
+
+	flush_icache_range(imv->imv, imv->imv + imv->size);
+
+	return 0;
+}
 
 /*
  * imv_mutex nests inside module_mutex. imv_mutex protects builtin
@@ -37,38 +55,6 @@ extern const struct __imv __stop___imv[];
  */
 static DEFINE_MUTEX(imv_mutex);
 
-static atomic_t wait_sync;
-
-struct ipi_loop_data {
-	long value;
-	const struct __imv *imv;
-} loop_data;
-
-static void ipi_busy_loop(void *arg)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	atomic_dec(&wait_sync);
-	do {
-		/* Make sure the wait_sync gets re-read */
-		smp_mb();
-	} while (atomic_read(&wait_sync) > loop_data.value);
-	atomic_dec(&wait_sync);
-	do {
-		/* Make sure the wait_sync gets re-read */
-		smp_mb();
-	} while (atomic_read(&wait_sync) > 0);
-	/*
-	 * Issuing a synchronizing instruction must be done on each CPU before
-	 * reenabling interrupts after modifying an instruction. Required by
-	 * Intel's errata.
-	 */
-	sync_core();
-	flush_icache_range(loop_data.imv->imv,
-		loop_data.imv->imv + loop_data.imv->size);
-	local_irq_restore(flags);
-}
 
 /**
  * apply_imv_update - update one immediate value
@@ -82,9 +68,6 @@ static void ipi_busy_loop(void *arg)
  */
 static int apply_imv_update(const struct __imv *imv)
 {
-	unsigned long flags;
-	long online_cpus;
-
 	/*
 	 * If the variable and the instruction have the same value, there is
 	 * nothing to do.
@@ -111,30 +94,8 @@ static int apply_imv_update(const struct __imv *imv)
 
 	if (imv_early_boot_complete) {
 		kernel_text_lock();
-		get_online_cpus();
-		online_cpus = num_online_cpus();
-		atomic_set(&wait_sync, 2 * online_cpus);
-		loop_data.value = online_cpus;
-		loop_data.imv = imv;
-		smp_call_function(ipi_busy_loop, NULL, 1, 0);
-		local_irq_save(flags);
-		atomic_dec(&wait_sync);
-		do {
-			/* Make sure the wait_sync gets re-read */
-			smp_mb();
-		} while (atomic_read(&wait_sync) > online_cpus);
-		text_poke((void *)imv->imv, (void *)imv->var,
-				imv->size);
-		/*
-		 * Make sure the modified instruction is seen by all CPUs before
-		 * we continue (visible to other CPUs and local interrupts).
-		 */
-		wmb();
-		atomic_dec(&wait_sync);
-		flush_icache_range(imv->imv,
-				imv->imv + imv->size);
-		local_irq_restore(flags);
-		put_online_cpus();
+		started = 0;
+		stop_machine_run(stop_machine_imv_update, (void *)imv, RUN_ALL);
 		kernel_text_unlock();
 	} else
 		text_poke_early((void *)imv->imv, (void *)imv->var,
--
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