Re: Possible to backport this vhost-net fix to 3.10?

[Eddie Chapman <eddie@ehuk.net>]

On 04/10/14 19:35, Michael S. Tsirkin wrote:
> On Sat, Oct 04, 2014 at 12:38:24AM +0100, Eddie Chapman wrote:
>> Hi,
>>
>> I've been regularly seeing on the 3.10 stable kernels the same problem as
>> reported by Romain Francoise here:
>> https://lkml.org/lkml/2013/1/23/492
>>
>> An example from my setup is at the bottom of this mail. It's a problem as
>> qemu fails to run when it hits this, only solution is to do all qemu
>> launches with vhost=off after it happens. It starts happening after the
>> machine has been running for a while and after a few VMs have been started.
>> I guess that is the fragmentation issue as the machine is never under any
>> serious memory pressure when it happens.
>>
>> I see this set of changes for 3.16 has a couple of fixes which appear to
>> address the problem:
>> https://lkml.org/lkml/2014/6/11/302
>>
>> I was just wondering if there are any plans to backport these to 3.10, or
>> even if it is actually possible (I'm not a kernel dev so wouldn't know)?
>>
>> If not, are there any other workarounds other than vhost=off?
>>
>> thanks,
>> Eddie
>
> Yes, these patches aren't hard to backport.
> Go ahead and post the backport, I'll review and ack.

Thanks Michael,

Actually I just discovered that Dmitry Petuhov backported 
23cc5a991c7a9fb7e6d6550e65cee4f4173111c5 ("vhost-net: extend device 
allocation to vmalloc") last month to the Proxmox 3.10 kernel
https://www.mail-archive.com/pve-devel@pve.proxmox.com/msg08873.html

He appears to have tested it quite thoroughly himself with a heavy 
workload, with no problems, though it hasn't gone into a Proxmox release 
yet.

His patch applies to vanilla kernel.org 3.10.55 with only slight 
fuzzines, so I've done some slight white space cleanup so it applies 
cleanly. vanilla 3.10.55 compiles fine on my machine without any errors 
or warnings with it. Is it OK (below)? Not sure it will meet stable 
submission rules?

Dmitry also says that d04257b07f2362d4eb550952d5bf5f4241a8046d 
("vhost-net: don't open-code kvfree") is not applicable in 3.10 because 
there's no open-coded kvfree() function (this appears in v3.15-rc5).

Have added Dmitry to CC.

thanks,
Eddie

--- a/drivers/vhost/net.c	2014-10-05 15:34:12.282126999 +0100
+++ b/drivers/vhost/net.c	2014-10-05 15:34:15.862140883 +0100
@@ -18,6 +18,7 @@
  #include <linux/rcupdate.h>
  #include <linux/file.h>
  #include <linux/slab.h>
+#include <linux/vmalloc.h>

  #include <linux/net.h>
  #include <linux/if_packet.h>
@@ -707,18 +708,30 @@
  	handle_rx(net);
  }

+static void vhost_net_free(void *addr)
+{
+	if (is_vmalloc_addr(addr))
+	vfree(addr);
+	else
+	kfree(addr);
+}
+
  static int vhost_net_open(struct inode *inode, struct file *f)
  {
-	struct vhost_net *n = kmalloc(sizeof *n, GFP_KERNEL);
+	struct vhost_net *n;
  	struct vhost_dev *dev;
  	struct vhost_virtqueue **vqs;
  	int r, i;

-	if (!n)
-		return -ENOMEM;
+		n = kmalloc(sizeof *n, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
+		if (!n) {
+			n = vmalloc(sizeof *n);
+			if (!n)
+			return -ENOMEM;
+		}
  	vqs = kmalloc(VHOST_NET_VQ_MAX * sizeof(*vqs), GFP_KERNEL);
  	if (!vqs) {
-		kfree(n);
+		vhost_net_free(n);
  		return -ENOMEM;
  	}

@@ -737,7 +750,7 @@
  	}
  	r = vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX);
  	if (r < 0) {
-		kfree(n);
+		vhost_net_free(n);
  		kfree(vqs);
  		return r;
  	}
@@ -840,7 +853,7 @@
  	 * since jobs can re-queue themselves. */
  	vhost_net_flush(n);
  	kfree(n->dev.vqs);
-	kfree(n);
+	vhost_net_free(n);
  	return 0;
  }


>
>
>> [1948751.794040] qemu-system-x86: page allocation failure: order:4,
>> mode:0x1040d0
>> [1948751.810341] CPU: 4 PID: 41198 Comm: qemu-system-x86 Not tainted
>> 3.10.53-rc1 #3
>> [1948751.826846] Hardware name: Intel Corporation S1200BTL/S1200BTL, BIOS
>> S1200BT.86B.02.00.0041.120520121743 12/05/2012
>> [1948751.847285]  0000000000000004 ffff8802eaf3b9d8 ffffffff8162ff4d
>> ffff8802eaf3ba68
>> [1948751.864257]  ffffffff810ab771 0000000000000001 ffff8802eaf3bb48
>> ffff8802eaf3ba68
>> [1948751.881209]  ffffffff810abe68 ffffffff81ca2f40 ffffffff00000000
>> 0000000200000040
>> [1948751.898276] Call Trace:
>> [1948751.909628]  [<ffffffff8162ff4d>] dump_stack+0x19/0x1c
>> [1948751.924284]  [<ffffffff810ab771>] warn_alloc_failed+0x111/0x126
>> [1948751.939774]  [<ffffffff810abe68>] ?
>> __alloc_pages_direct_compact+0x181/0x198
>> [1948751.956650]  [<ffffffff810ac5ae>] __alloc_pages_nodemask+0x72f/0x77c
>> [1948751.972853]  [<ffffffff810ac676>] __get_free_pages+0x12/0x41
>> [1948751.988297]  [<ffffffffa04ac71b>] vhost_net_open+0x23/0x171 [vhost_net]
>> [1948752.004938]  [<ffffffff8130d6c3>] misc_open+0x119/0x17d
>> [1948752.020111]  [<ffffffff810e99b4>] chrdev_open+0x134/0x155
>> [1948752.035604]  [<ffffffff81053193>] ? lg_local_unlock+0x1e/0x31
>> [1948752.051436]  [<ffffffff810e9880>] ? cdev_put+0x24/0x24
>> [1948752.066540]  [<ffffffff810e46b8>] do_dentry_open+0x15c/0x20f
>> [1948752.082214]  [<ffffffff810e484b>] finish_open+0x34/0x3f
>> [1948752.097234]  [<ffffffff810f2737>] do_last+0x996/0xbcb
>> [1948752.111983]  [<ffffffff810ef98e>] ? link_path_walk+0x5e/0x791
>> [1948752.127447]  [<ffffffff810f0296>] ? path_init+0x11d/0x403
>> [1948752.142517]  [<ffffffff810f2a32>] path_openat+0xc6/0x43b
>> [1948752.157207]  [<ffffffff81070f08>] ? __lock_acquire+0x9ae/0xa4a
>> [1948752.172369]  [<ffffffff815ac2ef>] ? rtnl_unlock+0x9/0xb
>> [1948752.186893]  [<ffffffff810f2eac>] do_filp_open+0x38/0x84
>> [1948752.201503]  [<ffffffff81633673>] ? _raw_spin_unlock+0x26/0x2a
>> [1948752.216719]  [<ffffffff810fdfef>] ? __alloc_fd+0xf6/0x10a
>> [1948752.231521]  [<ffffffff810e437c>] do_sys_open+0x114/0x1a6
>> [1948752.246396]  [<ffffffff810e4438>] SyS_open+0x19/0x1b
>> [1948752.260709]  [<ffffffff816341d2>] system_call_fastpath+0x16/0x1b
>