Poor performance with qemu

[Diego Calleja]

Hi, I'm using KVM, and the virtual disk (a 20 GB file using the raw
qemu format according to virt-manager and, of course, placed on a btrfs
filesystem, running the latest mainline git) is awfully slow, no matter
what OS is running inside the VM. The PCBSD installer says it's copying
data at a 40-50 KB/s rate. Is someone using KVM and having better numbers
than me? How can I help to debug this workload?
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[PATCH] fs/btrfs: Correct use after free

[Julia Lawall]

From: Julia Lawall ju...@diku.dk

If the kfree is executed, the dereference of range afterwards will
represent a use after free.  Added goto out, as done in the other nearby
error handling code.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// smpl
@@
expression x,e;
identifier f;
iterator I;
statement S;
@@

*kfree(x);
... when != x
when != x = e
when != I(x,...) S
*x-f
// /smpl

Signed-off-by: Julia Lawall ju...@diku.dk

---
 fs/btrfs/ioctl.c|1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2845c6c..dacbb52 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1375,6 +1375,7 @@ static int btrfs_ioctl_defrag(struct file *file, void 
__user *argp)
   sizeof(*range))) {
ret = -EFAULT;
kfree(range);
+   goto out;
}
/* compression requires us to start the IO */
if ((range-flags  BTRFS_DEFRAG_RANGE_COMPRESS)) {
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