[Patch 1 of 1] [xen-4.1.2] libxl: Seal tapdisk minor leak.

* [Patch 1 of 1] [xen-4.1.2] libxl: Seal tapdisk minor leak.
@ 2012-08-05 14:48 Dr. Greg Wettstein
  2012-08-07 15:14 ` Ian Jackson
  0 siblings, 1 reply; 5+ messages in thread
From: Dr. Greg Wettstein @ 2012-08-05 14:48 UTC (permalink / raw)
  To: xen-devel; +Cc: ian.jackson, keir

libxl: Seal tapdisk minor leak.

This patch needs to be applied on top of the following patch
to establish correct cleanup of a blktap2 based virtual disk:

libxl: attempt to cleanup tapdisk processes on disk backend destroy.

To implement correct cleanup of blktap devices in Xen 4.1.2.

This patch implements the release of the backend device before calling
for the destruction of the userspace component of the tapdisk device.

Without this patch the kernel xen-blkback driver deadlocks with
the tapdisk user control plane until the IPC channel is terminated by the
timeout on the select() call.  This results in a noticeable delay
in the termination of the guest and causes the blktap minor
number which had been allocated for the device to be orphaned.

Signed-off-by: Greg Wettstein <greg@enjellic.com>

diff -r b2b7a7a49af5 tools/libxl/libxl_blktap2.c

--- a/tools/libxl/libxl_blktap2.c	Sat Aug 04 16:17:08 2012 -0500
+++ b/tools/libxl/libxl_blktap2.c	Sun Aug 05 09:22:35 2012 -0500
@@ -59,6 +59,7 @@ void libxl__device_destroy_tapdisk(libxl
     char *path, *params, *type, *disk;
     int err;
     tap_list_t tap;
+    libxl_ctx *ctx = libxl__gc_owner(gc);
 
     path = libxl__sprintf(gc, "%s/tapdisk-params", be_path);
     if (!path) return;
@@ -75,5 +76,11 @@ void libxl__device_destroy_tapdisk(libxl
     err = tap_ctl_find(type, disk, &tap);
     if (err < 0) return;
 
+    /*
+     * Remove the instance of the backend device to avoid a deadlock with the
+     * removal of the tap device.
+     */
+    xs_rm(ctx->xsh, XBT_NULL, be_path);
+
     tap_ctl_destroy(tap.id, tap.minor);
 }
diff -r b2b7a7a49af5 tools/libxl/libxl_device.c
--- a/tools/libxl/libxl_device.c	Sat Aug 04 16:17:08 2012 -0500
+++ b/tools/libxl/libxl_device.c	Sun Aug 05 09:22:35 2012 -0500
@@ -250,8 +250,7 @@ int libxl__device_destroy(libxl_ctx *ctx
     if (!state)
         goto out;
     if (atoi(state) != 4) {
-        libxl__device_destroy_tapdisk(&gc, be_path);
-        xs_rm(ctx->xsh, XBT_NULL, be_path);
+	libxl__device_destroy_tapdisk(&gc, be_path);
         goto out;
     }
 
As always,
Dr. G.W. Wettstein, Ph.D.   Enjellic Systems Development, LLC.
4206 N. 19th Ave.           Specializing in information infra-structure
Fargo, ND  58102            development.
PH: 701-281-1686
FAX: 701-281-3949           EMAIL: greg@enjellic.com
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                                   Beyond Fear

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