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Subject[patch 21/55] drm/nouveau/gem: fix fence_sync race / oops
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Skeggs <bskeggs@redhat.com>

commit 525895ba388c949aa906f26e3ec5cb1ab041f56b upstream.

Due to a race it was possible for a fence to be destroyed while another
thread was trying to synchronise with it. If this happened in the fallback
non-semaphore path, it lead to the following oops due to fence->channel
being NULL.

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<fa9632ce>] nouveau_fence_update+0xe/0xe0 [nouveau]
*pde = a649c067
SMP
Modules linked in: fuse nouveau(O) ttm(O) drm_kms_helper(O) drm(O) mxm_wmi video wmi netconsole configfs lockd bnep bluetooth rfkill ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack ip6table_filter ip6_tables snd_hda_codec_realtek snd_hda_intel snd_hda_cobinfmt_misc uinput ata_generic pata_acpi pata_aet2c_algo_bit i2c_core [last unloaded: wmi]

Pid: 2255, comm: gnome-shell Tainted: G O 3.2.0-0.rc5.git0.1.fc17.i686 #1 System manufacturer System Product Name/M2A-VM
EIP: 0060:[<fa9632ce>] EFLAGS: 00010296 CPU: 1
EIP is at nouveau_fence_update+0xe/0xe0 [nouveau]
EAX: 00000000 EBX: ddfc6dd0 ECX: dd111580 EDX: 00000000
ESI: 00003e80 EDI: dd111580 EBP: dd121d00 ESP: dd121ce8
DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Process gnome-shell (pid: 2255, ti=dd120000 task=dd111580 task.ti=dd120000)
Stack:
7dc86c76 00000000 00003e80 ddfc6dd0 00003e80 dd111580 dd121d0c fa96371f
00000000 dd121d3c fa963773 dd111580 01000246 000ec53d 00000000 ddfc6dd0
00001f40 00000000 ddfc6dd0 00000010 dc7df840 dd121d6c fa9639a0 00000000
Call Trace:
[<fa96371f>] __nouveau_fence_signalled+0x1f/0x30 [nouveau]
[<fa963773>] __nouveau_fence_wait+0x43/0xd0 [nouveau]
[<fa9639a0>] nouveau_fence_sync+0x1a0/0x1c0 [nouveau]
[<fa964046>] validate_list+0x176/0x300 [nouveau]
[<f7d9c9c0>] ? ttm_bo_mem_put+0x30/0x30 [ttm]
[<fa964b8a>] nouveau_gem_ioctl_pushbuf+0x48a/0xfd0 [nouveau]
[<c0406481>] ? die+0x31/0x80
[<f7c93d98>] drm_ioctl+0x388/0x490 [drm]
[<c0406481>] ? die+0x31/0x80
[<fa964700>] ? nouveau_gem_ioctl_new+0x150/0x150 [nouveau]
[<c0635c7b>] ? file_has_perm+0xcb/0xe0
[<f7c93a10>] ? drm_copy_field+0x80/0x80 [drm]
[<c0564f56>] do_vfs_ioctl+0x86/0x5b0
[<c0406481>] ? die+0x31/0x80
[<c0635f22>] ? selinux_file_ioctl+0x62/0x130
[<c0554f30>] ? fget_light+0x30/0x340
[<c05654ef>] sys_ioctl+0x6f/0x80
[<c099e3a4>] syscall_call+0x7/0xb
[<c0406481>] ? die+0x31/0x80
[<c0406481>] ? die+0x31/0x80

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/nouveau/nouveau_gem.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/nouveau/nouveau_gem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
@@ -315,6 +315,25 @@ retry:
}

static int
+validate_sync(struct nouveau_channel *chan, struct nouveau_bo *nvbo)
+{
+ struct nouveau_fence *fence = NULL;
+ int ret = 0;
+
+ spin_lock(&nvbo->bo.bdev->fence_lock);
+ if (nvbo->bo.sync_obj)
+ fence = nouveau_fence_ref(nvbo->bo.sync_obj);
+ spin_unlock(&nvbo->bo.bdev->fence_lock);
+
+ if (fence) {
+ ret = nouveau_fence_sync(fence, chan);
+ nouveau_fence_unref(&fence);
+ }
+
+ return ret;
+}
+
+static int
validate_list(struct nouveau_channel *chan, struct list_head *list,
struct drm_nouveau_gem_pushbuf_bo *pbbo, uint64_t user_pbbo_ptr)
{
@@ -327,7 +346,7 @@ validate_list(struct nouveau_channel *ch
list_for_each_entry(nvbo, list, entry) {
struct drm_nouveau_gem_pushbuf_bo *b = &pbbo[nvbo->pbbo_index];

- ret = nouveau_fence_sync(nvbo->bo.sync_obj, chan);
+ ret = validate_sync(chan, nvbo);
if (unlikely(ret)) {
NV_ERROR(dev, "fail pre-validate sync\n");
return ret;
@@ -350,7 +369,7 @@ validate_list(struct nouveau_channel *ch
return ret;
}

- ret = nouveau_fence_sync(nvbo->bo.sync_obj, chan);
+ ret = validate_sync(chan, nvbo);
if (unlikely(ret)) {
NV_ERROR(dev, "fail post-validate sync\n");
return ret;



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