Re: That's pretty much it for 3.5.0

On 7/17/2012 3:18 PM, David Miller wrote:

From: John Fastabend <redacted>
Date: Tue, 17 Jul 2012 15:13:36 -0700

quoted

Perhaps the easiest way is to check net->count this should be zero
until setup_net is called.

if (!atomic_read(&init_net.count))
	return ret;

Won't work, setup_net() runs via a pure_initcall().

Why not must have missed something? cgroup_init() and
cgroup_early_init() both run before _initcall() routines are
called via kernel_init() so this will stop the update in
netprio from occurring.

And I don't see any race elsewhere for this.
--
To unsubscribe from this list: send the line "unsubscribe linux-wireless" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

On Tue, Jul 17, 2012 at 04:27:53PM -0700, John Fastabend wrote:

On 7/17/2012 3:18 PM, David Miller wrote:

quoted

From: John Fastabend <redacted>
Date: Tue, 17 Jul 2012 15:13:36 -0700

quoted

Perhaps the easiest way is to check net->count this should be zero
until setup_net is called.

if (!atomic_read(&init_net.count))
return ret;

Won't work, setup_net() runs via a pure_initcall().

Why not must have missed something? cgroup_init() and
cgroup_early_init() both run before _initcall() routines are
called via kernel_init() so this will stop the update in
netprio from occurring.

And I don't see any race elsewhere for this.

John, can you post the backtrace you got for this?  I replied to the patch that
you posted for this fix.  the cgroup subsystem has an early_init flag thats
supposed to prevent the initialization of cgroups that don't need initialization
until later (like via module_init() calls).
Neil

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

On Jul 18, 2012, at 6:04 AM, Neil Horman wrote:

John, can you post the backtrace you got for this?  I replied to the patch that
you posted for this fix.  the cgroup subsystem has an early_init flag thats
supposed to prevent the initialization of cgroups that don't need initialization
until later (like via module_init() calls).

Here is the backtrace that I get and below a patch that fixes it:

[    0.010958] Initializing cgroup subsys net_prio
[    0.011040] BUG: unable to handle kernel NULL pointer dereference at 0000000000000828
[    0.011998] IP: [<ffffffff814202c8>] update_netdev_tables+0x68/0xe0
[    0.011998] PGD 0 
[    0.011998] Oops: 0000 [#1] SMP 
[    0.011998] CPU 0 
[    0.011998] Modules linked in:
[    0.011998] 
[    0.011998] Pid: 0, comm: swapper/0 Not tainted 3.5.0-rc7-mdrlinux+ #10 Bochs Bochs
[    0.011998] RIP: 0010:[<ffffffff814202c8>]  [<ffffffff814202c8>] update_netdev_tables+0x68/0xe0
[    0.011998] RSP: 0000:ffffffff81a01e68  EFLAGS: 00010246
[    0.011998] RAX: 0000000000000000 RBX: fffffffffffffed0 RCX: 0000000000000000
[    0.011998] RDX: 0000000000000006 RSI: 2222222222222222 RDI: 2222222222222222
[    0.011998] RBP: ffffffff81a01e88 R08: 2222222222222222 R09: 2222222222222222
[    0.011998] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000001
[    0.011998] R13: 0000000000000000 R14: ffff88007ff608c0 R15: 00000000000143d0
[    0.011998] FS:  0000000000000000(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000
[    0.011998] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[    0.011998] CR2: 0000000000000828 CR3: 0000000001a0b000 CR4: 00000000000006b0
[    0.011998] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    0.011998] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[    0.011998] Process swapper/0 (pid: 0, threadinfo ffffffff81a00000, task ffffffff81a13420)
[    0.011998] Stack:
[    0.011998]  ffffffff81a88020 0000000000000000 ffff88007d3a38f0 fffffffffffffff4
[    0.011998]  ffffffff81a01ec8 ffffffff814203cd ffff88007ff608c0 ffffffff817d8e9a
[    0.011998]  ffffffff81a88cd8 ffffffff81a88020 ffffffff81a88020 ffffffff81b010a0
[    0.011998] Call Trace:
[    0.011998]  [<ffffffff814203cd>] cgrp_create+0x8d/0xc0
[    0.011998]  [<ffffffff81ade14a>] cgroup_init_subsys+0x80/0x126
[    0.011998]  [<ffffffff81ade380>] cgroup_init+0x36/0x117
[    0.011998]  [<ffffffff81acab71>] start_kernel+0x32e/0x34f
[    0.011998]  [<ffffffff81aca6d5>] ? repair_env_string+0x5a/0x5a
[    0.011998]  [<ffffffff81aca346>] x86_64_start_reservations+0x101/0x105
[    0.011998]  [<ffffffff81aca120>] ? early_idt_handlers+0x120/0x120
[    0.011998]  [<ffffffff81aca417>] x86_64_start_kernel+0xcd/0xdc
[    0.011998] Code: 0f 1f 00 48 8b 83 30 01 00 00 48 8d 98 d0 fe ff ff 48 3d a8 e8 52 82 74 3a e8 25 db c3 ff 85 c0 74 09 80 3d bb 3d 68 00 00 74 40 <48> 8b 83 58 09 00 00 48 85 c0 74 cc 44 3b 60 10 76 c6 44 89 e6 
[    0.011998] RIP  [<ffffffff814202c8>] update_netdev_tables+0x68/0xe0
[    0.011998]  RSP <ffffffff81a01e68>
[    0.011998] CR2: 0000000000000828
[    0.012009] ---[ end trace a7919e7f17c0a725 ]---
[    0.012601] Kernel panic - not syncing: Attempted to kill the idle task!

The following change simply statically initializes init_net.dev_base_head. I copied and pasted it into the email, so this rendering may not work, but I can send it if this approach looks reasonable. I have verified that it resolves the issue above.

diff --git a/net/core/dev.c b/net/core/dev.c
index 0f28a9e..db1ba61 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -6283,8 +6283,6 @@ static struct hlist_head *netdev_create_hash(void)
 /* Initialize per network namespace state */
 static int __net_init netdev_init(struct net *net)
 {
-       INIT_LIST_HEAD(&net->dev_base_head);
-
        net->dev_name_head = netdev_create_hash();
        if (net->dev_name_head == NULL)
                goto err_name;

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index dddbacb..42f1e1c 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c

@@ -27,7 +27,9 @@ static DEFINE_MUTEX(net_mutex);
 LIST_HEAD(net_namespace_list);
 EXPORT_SYMBOL_GPL(net_namespace_list);
 
-struct net init_net;
+struct net init_net = {
+       .dev_base_head = LIST_HEAD_INIT(init_net.dev_base_head),
+};
 EXPORT_SYMBOL(init_net);
 
 #define INITIAL_NET_GEN_PTRS   13 /* +1 for len +2 for rcu_head */

-- 
Mark Rustad, LAN Access Division, Intel Corporation

On Wed, 2012-07-18 at 17:36 +0000, Rustad, Mark D wrote:

	if (net != &init_net)
		INIT_LIST_HEAD(&net->dev_base_head);

On Jul 18, 2012, at 10:55 AM, Eric Dumazet wrote:

On Wed, 2012-07-18 at 17:36 +0000, Rustad, Mark D wrote:

quoted

The following change simply statically initializes init_net.dev_base_head. I copied and pasted it into the email, so this rendering may not work, but I can send it if this approach looks reasonable. I have verified that it resolves the issue above.

diff --git a/net/core/dev.c b/net/core/dev.c
index 0f28a9e..db1ba61 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -6283,8 +6283,6 @@ static struct hlist_head *netdev_create_hash(void)

/* Initialize per network namespace state */
static int __net_init netdev_init(struct net *net)
{
-       INIT_LIST_HEAD(&net->dev_base_head);
-

	if (net != &init_net)
		INIT_LIST_HEAD(&net->dev_base_head);

Ooooh. Good catch.

quoted

       net->dev_name_head = netdev_create_hash();
       if (net->dev_name_head == NULL)
               goto err_name;

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index dddbacb..42f1e1c 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c

@@ -27,7 +27,9 @@ static DEFINE_MUTEX(net_mutex);

LIST_HEAD(net_namespace_list);
EXPORT_SYMBOL_GPL(net_namespace_list);

-struct net init_net;
+struct net init_net = {
+       .dev_base_head = LIST_HEAD_INIT(init_net.dev_base_head),
+};
EXPORT_SYMBOL(init_net);

#define INITIAL_NET_GEN_PTRS   13 /* +1 for len +2 for rcu_head */

If this looks like a good change, I can send the patch. Is there any concern about init_net going from bss to data?

-- 
Mark Rustad, LAN Access Division, Intel Corporation

--
To unsubscribe from this list: send the line "unsubscribe linux-wireless" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html