Fix RandR leasing for more than 1 simultaneously active lease.

Due to a switched order of parameters in the xorg_list_add()
call inside ProcRRCreateLease(), adding a new lease for RandR
output leasing does not actually add the new RRLeasePtr lease
record to the list of existing leases for a X-Screen, but instead
replaces the existing list with a new list that has the new lease
as the only element, and probably leaks a bit of memory.

Therefore the server "forgets" all active leases for a screen,
except for the last added lease. If multiple leases are created
in a session, then destruction of all leases but the last one
will fail in many cases, e.g., during server shutdown in
RRCloseScreen(), or resource destruction, e.g., in
RRCrtcDestroyResource().

Most importantly, it fails if a client simply close(fd)'es the
DRM master descriptor to release a lease, quits, gets killed or
crashes. In this case the kernel will destroy the lease and shut
down the display output, then send a lease event via udev to the
ddx, which e.g., in the modesetting-ddx will trigger a call to
drmmode_validate_leases().

That function is supposed to detect the released lease and tell
the server to terminate the lease on the server side as well,
via xf86CrtcLeaseTerminated(), but this doesn't happen for all
the leases the server has forgotten. The end result is a dead
video output, as the server won't reinitialize the crtc's
corresponding to the terminated but forgotten lease.

This bug was observed when using the amdvlk AMD OSS Vulkan
driver and trying to lease multiple VKDisplay's, and also
under Mesa radv, as both Mesa Vulkan/WSI/Display and amdvlk
terminate leases by simply close()ing the lease fd, not by
sending explicit RandR protocol requests to free leases.

Leasing worked, but ending a session with multiple active
leases ended in a lot of unpleasant darkness.

Fixing the wrong argument order to xorg_list_add() fixes the
problem. Tested on single-X-Screen and dual-X-Screen setups,
with one, two or three active leases.

Please merge this for the upcoming server 21.1 branch.
Merging into server 1.20 would also make a lot of sense.

Fixes: e4e3447603b5fd3a38a92c3f972396d1f81168ad
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Keith Packard <keithp@keithp.com>
(cherry picked from commit f467f85ca1f780d5c7cf3c20888e399708d761ac)

1 files changed, 1 insertions, 1 deletions

diff --git a/randr/rrlease.c b/randr/rrlease.c
index e25d9ca99..11ba96f24 100644
--- a/randr/rrlease.c
+++ b/randr/rrlease.c
@@ -295,7 +295,7 @@ ProcRRCreateLease(ClientPtr client)
     if (rc != Success)
         goto bail_lease;
 
-    xorg_list_add(&scr_priv->leases, &lease->list);
+    xorg_list_add(&lease->list, &scr_priv->leases);
 
     if (!AddResource(stuff->lid, RRLeaseType, lease)) {
         close(fd);