Fixing gang ABD child removal race condition

On linux the list debug code has been setting off a failure when
checking that the node->next->prev value is pointing back at the node.
At times this check evaluates to 0xdead. When removing a child from a
gang ABD we must acquire the child's abd_mtx to make sure that the
same ABD is not being added to another gang ABD while it is being
removed from a gang ABD. This fixes a race condition when checking
if an ABDs link is already active and part of another gang ABD before
adding it to a gang.

Added additional debug code for the gang ABD in abd_verify() to make
sure each child ABD has active links. Also check to make sure another
gang ABD is not added to a gang ABD.

Reviewed-by: Serapheim Dimitropoulos <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Matt Ahrens <[email protected]>
Signed-off-by: Brian Atkinson <[email protected]>
Closes #10511 

1 files changed, 1 insertions, 0 deletions

diff --git a/module/os/freebsd/spl/list.c b/module/os/freebsd/spl/list.c
index e8db13a5c..21230b2ad 100644
--- a/module/os/freebsd/spl/list.c
+++ b/module/os/freebsd/spl/list.c
@@ -235,6 +235,7 @@ list_link_init(list_node_t *link)
 int
 list_link_active(list_node_t *link)
 {
+	EQUIV(link->list_next == NULL, link->list_prev == NULL);
 	return (link->list_next != NULL);
 }