There are few defects in vga_get() related to signal hadning:
- we shouldn't check for pending signals for TASK_UNINTERRUPTIBLE
case;
- if we found pending signal we must remove ourself from wait queue
and change task state back to running;
- -ERESTARTSYS is more appropriate, I guess.
Signed-off-by: Kirill A. Shutemov <[email protected]>
---
Alex, I try to get KVM with VGA passthrough working properly. I have i915
(HD 4600) on the host and GTX 580 for the guest. The guest GPU is not
capabale of EFI, so I have to use x-vga=on. It's kinda work with your
patch for i915.enable_hd_vgaarb=1. But guest refuse to initialize the GPU
after KVM was not shut down correctly, resulting in host crash like this:
BUG: unable to handle kernel paging request at ffff880870187ed8
IP: [<ffff880870187ed8>] 0xffff880870187ed8
PGD 2129067 PUD 80000008400001e3
Oops: 0011 [#1] PREEMPT SMP
Modules linked in: iwlmvm iwlwifi
CPU: 6 PID: 3983 Comm: qemu-system-x86 Not tainted 4.3.0-gentoo #6
Hardware name: Gigabyte Technology Co., Ltd. Z87X-UD7 TH/Z87X-UD7 TH-CF, BIOS F5a 06/12/2014
task: ffff88087a910000 ti: ffff8808632c0000 task.ti: ffff8808632c0000
RIP: 0010:[<ffff880870187ed8>] [<ffff880870187ed8>] 0xffff880870187ed8
RSP: 0018:ffff8808632c3d08 EFLAGS: 00010006
RAX: ffff880870187db0 RBX: 0000000070187f58 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff880870187db0
RBP: ffff8808632c3d48 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000103c0 R11: 0000000000000293 R12: ffffffff81ea03c8
R13: ffffffff8104c7cb R14: 0000000000000000 R15: 0000000000000003
FS: 00007f984f9b2700(0000) GS:ffff88089f380000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff880870187ed8 CR3: 00000008645f8000 CR4: 00000000001426e0
Stack:
ffffffff810cc83d 00000000632c3d28 0000000000000000 ffffffff81ea03c0
0000000000000046 0000000000000003 0000000000000000 0000000000000000
ffff8808632c3d80 ffffffff810cca44 ffff88087af63800 0000000000000286
Call Trace:
[<ffffffff810cc83d>] ? __wake_up_common+0x4d/0x80
[<ffffffff810cca44>] __wake_up+0x34/0x50
[<ffffffff815d99e3>] __vga_put+0x73/0xd0
[<ffffffff815d9db4>] vga_put+0x54/0x80
[<ffffffff8169d042>] vfio_pci_vga_rw+0x1d2/0x220
[<ffffffff8169a7f3>] vfio_pci_rw+0x33/0x60
[<ffffffff8169abf7>] vfio_pci_write+0x17/0x20
[<ffffffff816966a6>] vfio_device_fops_write+0x26/0x30
[<ffffffff811a4b23>] __vfs_write+0x23/0xe0
[<ffffffff811a4a53>] ? __vfs_read+0x23/0xd0
[<ffffffff811b6e35>] ? do_vfs_ioctl+0x2b5/0x490
[<ffffffff811a5194>] vfs_write+0xa4/0x190
[<ffffffff811a5fa6>] SyS_pwrite64+0x66/0xa0
[<ffffffff819a17d7>] entry_SYSCALL_64_fastpath+0x12/0x6a
Code: 88 ff ff e0 7e 18 70 08 88 ff ff 00 8c 57 76 08 88 ff ff 20 7f 18 70 08 88 ff ff 08 7f 18 70 08 88 ff ff 94 51 1a 81 ff ff ff ff <09> 00 00 00 00 00 00 00 01 8c 57 76 08 88 ff ff 00 8c 57 76 08
RIP [<ffff880870187ed8>] 0xffff880870187ed8
RSP <ffff8808632c3d08>
CR2: ffff880870187ed8
The patch fixes the crash, but doesn't help with getting GPU in guest
working again.
Any ideas?
---
drivers/gpu/vga/vgaarb.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
index 3166e4bc4eb6..9abcaa53bd25 100644
--- a/drivers/gpu/vga/vgaarb.c
+++ b/drivers/gpu/vga/vgaarb.c
@@ -395,8 +395,10 @@ int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
set_current_state(interruptible ?
TASK_INTERRUPTIBLE :
TASK_UNINTERRUPTIBLE);
- if (signal_pending(current)) {
- rc = -EINTR;
+ if (interruptible && signal_pending(current)) {
+ __set_current_state(TASK_RUNNING);
+ remove_wait_queue(&vga_wait_queue, &wait);
+ rc = -ERESTARTSYS;
break;
}
schedule();
--
2.6.3
On Mon, Nov 30, 2015 at 04:17:31AM +0200, Kirill A. Shutemov wrote:
> There are few defects in vga_get() related to signal hadning:
>
> - we shouldn't check for pending signals for TASK_UNINTERRUPTIBLE
> case;
>
> - if we found pending signal we must remove ourself from wait queue
> and change task state back to running;
>
> - -ERESTARTSYS is more appropriate, I guess.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
Ping?
David, this patch fixes crash. It would be nice to get it into 4.4.
> ---
>
> Alex, I try to get KVM with VGA passthrough working properly. I have i915
> (HD 4600) on the host and GTX 580 for the guest. The guest GPU is not
> capabale of EFI, so I have to use x-vga=on. It's kinda work with your
> patch for i915.enable_hd_vgaarb=1. But guest refuse to initialize the GPU
> after KVM was not shut down correctly, resulting in host crash like this:
>
> BUG: unable to handle kernel paging request at ffff880870187ed8
> IP: [<ffff880870187ed8>] 0xffff880870187ed8
> PGD 2129067 PUD 80000008400001e3
> Oops: 0011 [#1] PREEMPT SMP
> Modules linked in: iwlmvm iwlwifi
> CPU: 6 PID: 3983 Comm: qemu-system-x86 Not tainted 4.3.0-gentoo #6
> Hardware name: Gigabyte Technology Co., Ltd. Z87X-UD7 TH/Z87X-UD7 TH-CF, BIOS F5a 06/12/2014
> task: ffff88087a910000 ti: ffff8808632c0000 task.ti: ffff8808632c0000
> RIP: 0010:[<ffff880870187ed8>] [<ffff880870187ed8>] 0xffff880870187ed8
> RSP: 0018:ffff8808632c3d08 EFLAGS: 00010006
> RAX: ffff880870187db0 RBX: 0000000070187f58 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff880870187db0
> RBP: ffff8808632c3d48 R08: 0000000000000000 R09: 0000000000000000
> R10: 00000000000103c0 R11: 0000000000000293 R12: ffffffff81ea03c8
> R13: ffffffff8104c7cb R14: 0000000000000000 R15: 0000000000000003
> FS: 00007f984f9b2700(0000) GS:ffff88089f380000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff880870187ed8 CR3: 00000008645f8000 CR4: 00000000001426e0
> Stack:
> ffffffff810cc83d 00000000632c3d28 0000000000000000 ffffffff81ea03c0
> 0000000000000046 0000000000000003 0000000000000000 0000000000000000
> ffff8808632c3d80 ffffffff810cca44 ffff88087af63800 0000000000000286
> Call Trace:
> [<ffffffff810cc83d>] ? __wake_up_common+0x4d/0x80
> [<ffffffff810cca44>] __wake_up+0x34/0x50
> [<ffffffff815d99e3>] __vga_put+0x73/0xd0
> [<ffffffff815d9db4>] vga_put+0x54/0x80
> [<ffffffff8169d042>] vfio_pci_vga_rw+0x1d2/0x220
> [<ffffffff8169a7f3>] vfio_pci_rw+0x33/0x60
> [<ffffffff8169abf7>] vfio_pci_write+0x17/0x20
> [<ffffffff816966a6>] vfio_device_fops_write+0x26/0x30
> [<ffffffff811a4b23>] __vfs_write+0x23/0xe0
> [<ffffffff811a4a53>] ? __vfs_read+0x23/0xd0
> [<ffffffff811b6e35>] ? do_vfs_ioctl+0x2b5/0x490
> [<ffffffff811a5194>] vfs_write+0xa4/0x190
> [<ffffffff811a5fa6>] SyS_pwrite64+0x66/0xa0
> [<ffffffff819a17d7>] entry_SYSCALL_64_fastpath+0x12/0x6a
> Code: 88 ff ff e0 7e 18 70 08 88 ff ff 00 8c 57 76 08 88 ff ff 20 7f 18 70 08 88 ff ff 08 7f 18 70 08 88 ff ff 94 51 1a 81 ff ff ff ff <09> 00 00 00 00 00 00 00 01 8c 57 76 08 88 ff ff 00 8c 57 76 08
> RIP [<ffff880870187ed8>] 0xffff880870187ed8
> RSP <ffff8808632c3d08>
> CR2: ffff880870187ed8
>
> The patch fixes the crash, but doesn't help with getting GPU in guest
> working again.
>
> Any ideas?
>
> ---
> drivers/gpu/vga/vgaarb.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index 3166e4bc4eb6..9abcaa53bd25 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -395,8 +395,10 @@ int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
> set_current_state(interruptible ?
> TASK_INTERRUPTIBLE :
> TASK_UNINTERRUPTIBLE);
> - if (signal_pending(current)) {
> - rc = -EINTR;
> + if (interruptible && signal_pending(current)) {
> + __set_current_state(TASK_RUNNING);
> + remove_wait_queue(&vga_wait_queue, &wait);
> + rc = -ERESTARTSYS;
> break;
> }
> schedule();
> --
> 2.6.3
>
--
Kirill A. Shutemov
Hi
On Mon, Nov 30, 2015 at 3:17 AM, Kirill A. Shutemov
<[email protected]> wrote:
> There are few defects in vga_get() related to signal hadning:
>
> - we shouldn't check for pending signals for TASK_UNINTERRUPTIBLE
> case;
>
> - if we found pending signal we must remove ourself from wait queue
> and change task state back to running;
>
> - -ERESTARTSYS is more appropriate, I guess.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> ---
>
> Alex, I try to get KVM with VGA passthrough working properly. I have i915
> (HD 4600) on the host and GTX 580 for the guest. The guest GPU is not
> capabale of EFI, so I have to use x-vga=on. It's kinda work with your
> patch for i915.enable_hd_vgaarb=1. But guest refuse to initialize the GPU
> after KVM was not shut down correctly, resulting in host crash like this:
>
> BUG: unable to handle kernel paging request at ffff880870187ed8
> IP: [<ffff880870187ed8>] 0xffff880870187ed8
> PGD 2129067 PUD 80000008400001e3
> Oops: 0011 [#1] PREEMPT SMP
> Modules linked in: iwlmvm iwlwifi
> CPU: 6 PID: 3983 Comm: qemu-system-x86 Not tainted 4.3.0-gentoo #6
> Hardware name: Gigabyte Technology Co., Ltd. Z87X-UD7 TH/Z87X-UD7 TH-CF, BIOS F5a 06/12/2014
> task: ffff88087a910000 ti: ffff8808632c0000 task.ti: ffff8808632c0000
> RIP: 0010:[<ffff880870187ed8>] [<ffff880870187ed8>] 0xffff880870187ed8
> RSP: 0018:ffff8808632c3d08 EFLAGS: 00010006
> RAX: ffff880870187db0 RBX: 0000000070187f58 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff880870187db0
> RBP: ffff8808632c3d48 R08: 0000000000000000 R09: 0000000000000000
> R10: 00000000000103c0 R11: 0000000000000293 R12: ffffffff81ea03c8
> R13: ffffffff8104c7cb R14: 0000000000000000 R15: 0000000000000003
> FS: 00007f984f9b2700(0000) GS:ffff88089f380000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffff880870187ed8 CR3: 00000008645f8000 CR4: 00000000001426e0
> Stack:
> ffffffff810cc83d 00000000632c3d28 0000000000000000 ffffffff81ea03c0
> 0000000000000046 0000000000000003 0000000000000000 0000000000000000
> ffff8808632c3d80 ffffffff810cca44 ffff88087af63800 0000000000000286
> Call Trace:
> [<ffffffff810cc83d>] ? __wake_up_common+0x4d/0x80
> [<ffffffff810cca44>] __wake_up+0x34/0x50
> [<ffffffff815d99e3>] __vga_put+0x73/0xd0
> [<ffffffff815d9db4>] vga_put+0x54/0x80
> [<ffffffff8169d042>] vfio_pci_vga_rw+0x1d2/0x220
> [<ffffffff8169a7f3>] vfio_pci_rw+0x33/0x60
> [<ffffffff8169abf7>] vfio_pci_write+0x17/0x20
> [<ffffffff816966a6>] vfio_device_fops_write+0x26/0x30
> [<ffffffff811a4b23>] __vfs_write+0x23/0xe0
> [<ffffffff811a4a53>] ? __vfs_read+0x23/0xd0
> [<ffffffff811b6e35>] ? do_vfs_ioctl+0x2b5/0x490
> [<ffffffff811a5194>] vfs_write+0xa4/0x190
> [<ffffffff811a5fa6>] SyS_pwrite64+0x66/0xa0
> [<ffffffff819a17d7>] entry_SYSCALL_64_fastpath+0x12/0x6a
> Code: 88 ff ff e0 7e 18 70 08 88 ff ff 00 8c 57 76 08 88 ff ff 20 7f 18 70 08 88 ff ff 08 7f 18 70 08 88 ff ff 94 51 1a 81 ff ff ff ff <09> 00 00 00 00 00 00 00 01 8c 57 76 08 88 ff ff 00 8c 57 76 08
> RIP [<ffff880870187ed8>] 0xffff880870187ed8
> RSP <ffff8808632c3d08>
> CR2: ffff880870187ed8
>
> The patch fixes the crash, but doesn't help with getting GPU in guest
> working again.
>
> Any ideas?
>
> ---
> drivers/gpu/vga/vgaarb.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index 3166e4bc4eb6..9abcaa53bd25 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -395,8 +395,10 @@ int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
> set_current_state(interruptible ?
> TASK_INTERRUPTIBLE :
> TASK_UNINTERRUPTIBLE);
> - if (signal_pending(current)) {
> - rc = -EINTR;
> + if (interruptible && signal_pending(current)) {
> + __set_current_state(TASK_RUNNING);
> + remove_wait_queue(&vga_wait_queue, &wait);
> + rc = -ERESTARTSYS;
> break;
All 3 points are valid, and the patch looks good to me:
Reviewed-by: David Herrmann <[email protected]>
However, there seems to be a race between vga_lock and putting the
thread asleep. We should fix that as well. See the hunk below
(completely untested.. why is VGA still in use? *sigh*).
Thanks
David
diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
index a0b4334..82cf1e3 100644
--- a/drivers/gpu/vga/vgaarb.c
+++ b/drivers/gpu/vga/vgaarb.c
@@ -359,8 +359,8 @@ static void __vga_put
int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
{
struct vga_device *vgadev, *conflict;
+ DECLARE_WAITQUEUE(wait, current);
unsigned long flags;
- wait_queue_t wait;
int rc = 0;
vga_check_first_use();
@@ -371,6 +371,11 @@ int vga_get
return 0;
for (;;) {
+ add_wait_queue(&vga_wait_queue, &wait);
+ set_current_state(interruptible ?
+ TASK_INTERRUPTIBLE :
+ TASK_UNINTERRUPTIBLE);
+
spin_lock_irqsave(&vga_lock, flags);
vgadev = vgadev_find(pdev);
if (vgadev == NULL) {
@@ -383,25 +388,22 @@ int vga_get(struct pci_dev *pdev, unsigned int
rsrc, int interruptible)
if (conflict == NULL)
break;
-
/* We have a conflict, we wait until somebody kicks the
* work queue. Currently we have one work queue that we
* kick each time some resources are released, but it would
* be fairly easy to have a per device one so that we only
* need to attach to the conflicting device
*/
- init_waitqueue_entry(&wait, current);
- add_wait_queue(&vga_wait_queue, &wait);
- set_current_state(interruptible ?
- TASK_INTERRUPTIBLE :
- TASK_UNINTERRUPTIBLE);
- if (signal_pending(current)) {
- rc = -EINTR;
+ if (interruptible && signal_pending(current)) {
+ rc = -ERESTARTSYS;
break;
}
schedule();
remove_wait_queue(&vga_wait_queue, &wait);
}
+
+ __set_current_state(TASK_RUNNING);
+ remove_wait_queue(&vga_wait_queue, &wait);
return rc;
}
EXPORT_SYMBOL(vga_get);
On Thu, Dec 10, 2015 at 11:28:58AM +0100, David Herrmann wrote:
> Hi
>
> On Mon, Nov 30, 2015 at 3:17 AM, Kirill A. Shutemov
> <[email protected]> wrote:
> > There are few defects in vga_get() related to signal hadning:
> >
> > - we shouldn't check for pending signals for TASK_UNINTERRUPTIBLE
> > case;
> >
> > - if we found pending signal we must remove ourself from wait queue
> > and change task state back to running;
> >
> > - -ERESTARTSYS is more appropriate, I guess.
> >
> > Signed-off-by: Kirill A. Shutemov <[email protected]>
> > ---
> >
> > Alex, I try to get KVM with VGA passthrough working properly. I have i915
> > (HD 4600) on the host and GTX 580 for the guest. The guest GPU is not
> > capabale of EFI, so I have to use x-vga=on. It's kinda work with your
> > patch for i915.enable_hd_vgaarb=1. But guest refuse to initialize the GPU
> > after KVM was not shut down correctly, resulting in host crash like this:
> >
> > BUG: unable to handle kernel paging request at ffff880870187ed8
> > IP: [<ffff880870187ed8>] 0xffff880870187ed8
> > PGD 2129067 PUD 80000008400001e3
> > Oops: 0011 [#1] PREEMPT SMP
> > Modules linked in: iwlmvm iwlwifi
> > CPU: 6 PID: 3983 Comm: qemu-system-x86 Not tainted 4.3.0-gentoo #6
> > Hardware name: Gigabyte Technology Co., Ltd. Z87X-UD7 TH/Z87X-UD7 TH-CF, BIOS F5a 06/12/2014
> > task: ffff88087a910000 ti: ffff8808632c0000 task.ti: ffff8808632c0000
> > RIP: 0010:[<ffff880870187ed8>] [<ffff880870187ed8>] 0xffff880870187ed8
> > RSP: 0018:ffff8808632c3d08 EFLAGS: 00010006
> > RAX: ffff880870187db0 RBX: 0000000070187f58 RCX: 0000000000000000
> > RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff880870187db0
> > RBP: ffff8808632c3d48 R08: 0000000000000000 R09: 0000000000000000
> > R10: 00000000000103c0 R11: 0000000000000293 R12: ffffffff81ea03c8
> > R13: ffffffff8104c7cb R14: 0000000000000000 R15: 0000000000000003
> > FS: 00007f984f9b2700(0000) GS:ffff88089f380000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: ffff880870187ed8 CR3: 00000008645f8000 CR4: 00000000001426e0
> > Stack:
> > ffffffff810cc83d 00000000632c3d28 0000000000000000 ffffffff81ea03c0
> > 0000000000000046 0000000000000003 0000000000000000 0000000000000000
> > ffff8808632c3d80 ffffffff810cca44 ffff88087af63800 0000000000000286
> > Call Trace:
> > [<ffffffff810cc83d>] ? __wake_up_common+0x4d/0x80
> > [<ffffffff810cca44>] __wake_up+0x34/0x50
> > [<ffffffff815d99e3>] __vga_put+0x73/0xd0
> > [<ffffffff815d9db4>] vga_put+0x54/0x80
> > [<ffffffff8169d042>] vfio_pci_vga_rw+0x1d2/0x220
> > [<ffffffff8169a7f3>] vfio_pci_rw+0x33/0x60
> > [<ffffffff8169abf7>] vfio_pci_write+0x17/0x20
> > [<ffffffff816966a6>] vfio_device_fops_write+0x26/0x30
> > [<ffffffff811a4b23>] __vfs_write+0x23/0xe0
> > [<ffffffff811a4a53>] ? __vfs_read+0x23/0xd0
> > [<ffffffff811b6e35>] ? do_vfs_ioctl+0x2b5/0x490
> > [<ffffffff811a5194>] vfs_write+0xa4/0x190
> > [<ffffffff811a5fa6>] SyS_pwrite64+0x66/0xa0
> > [<ffffffff819a17d7>] entry_SYSCALL_64_fastpath+0x12/0x6a
> > Code: 88 ff ff e0 7e 18 70 08 88 ff ff 00 8c 57 76 08 88 ff ff 20 7f 18 70 08 88 ff ff 08 7f 18 70 08 88 ff ff 94 51 1a 81 ff ff ff ff <09> 00 00 00 00 00 00 00 01 8c 57 76 08 88 ff ff 00 8c 57 76 08
> > RIP [<ffff880870187ed8>] 0xffff880870187ed8
> > RSP <ffff8808632c3d08>
> > CR2: ffff880870187ed8
> >
> > The patch fixes the crash, but doesn't help with getting GPU in guest
> > working again.
> >
> > Any ideas?
> >
> > ---
> > drivers/gpu/vga/vgaarb.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> > index 3166e4bc4eb6..9abcaa53bd25 100644
> > --- a/drivers/gpu/vga/vgaarb.c
> > +++ b/drivers/gpu/vga/vgaarb.c
> > @@ -395,8 +395,10 @@ int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
> > set_current_state(interruptible ?
> > TASK_INTERRUPTIBLE :
> > TASK_UNINTERRUPTIBLE);
> > - if (signal_pending(current)) {
> > - rc = -EINTR;
> > + if (interruptible && signal_pending(current)) {
> > + __set_current_state(TASK_RUNNING);
> > + remove_wait_queue(&vga_wait_queue, &wait);
> > + rc = -ERESTARTSYS;
> > break;
>
> All 3 points are valid, and the patch looks good to me:
>
> Reviewed-by: David Herrmann <[email protected]>
>
> However, there seems to be a race between vga_lock and putting the
> thread asleep.
I'm not sure I understand the race you're talking about.
Could you elaborate?
--
Kirill A. Shutemov
Hi
On Mon, Dec 14, 2015 at 9:19 AM, Kirill A. Shutemov
<[email protected]> wrote:
> On Thu, Dec 10, 2015 at 11:28:58AM +0100, David Herrmann wrote:
>> Hi
>>
>> On Mon, Nov 30, 2015 at 3:17 AM, Kirill A. Shutemov
>> <[email protected]> wrote:
>> > There are few defects in vga_get() related to signal hadning:
>> >
>> > - we shouldn't check for pending signals for TASK_UNINTERRUPTIBLE
>> > case;
>> >
>> > - if we found pending signal we must remove ourself from wait queue
>> > and change task state back to running;
>> >
>> > - -ERESTARTSYS is more appropriate, I guess.
>> >
>> > Signed-off-by: Kirill A. Shutemov <[email protected]>
>> > ---
>> >
>> > Alex, I try to get KVM with VGA passthrough working properly. I have i915
>> > (HD 4600) on the host and GTX 580 for the guest. The guest GPU is not
>> > capabale of EFI, so I have to use x-vga=on. It's kinda work with your
>> > patch for i915.enable_hd_vgaarb=1. But guest refuse to initialize the GPU
>> > after KVM was not shut down correctly, resulting in host crash like this:
>> >
>> > BUG: unable to handle kernel paging request at ffff880870187ed8
>> > IP: [<ffff880870187ed8>] 0xffff880870187ed8
>> > PGD 2129067 PUD 80000008400001e3
>> > Oops: 0011 [#1] PREEMPT SMP
>> > Modules linked in: iwlmvm iwlwifi
>> > CPU: 6 PID: 3983 Comm: qemu-system-x86 Not tainted 4.3.0-gentoo #6
>> > Hardware name: Gigabyte Technology Co., Ltd. Z87X-UD7 TH/Z87X-UD7 TH-CF, BIOS F5a 06/12/2014
>> > task: ffff88087a910000 ti: ffff8808632c0000 task.ti: ffff8808632c0000
>> > RIP: 0010:[<ffff880870187ed8>] [<ffff880870187ed8>] 0xffff880870187ed8
>> > RSP: 0018:ffff8808632c3d08 EFLAGS: 00010006
>> > RAX: ffff880870187db0 RBX: 0000000070187f58 RCX: 0000000000000000
>> > RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff880870187db0
>> > RBP: ffff8808632c3d48 R08: 0000000000000000 R09: 0000000000000000
>> > R10: 00000000000103c0 R11: 0000000000000293 R12: ffffffff81ea03c8
>> > R13: ffffffff8104c7cb R14: 0000000000000000 R15: 0000000000000003
>> > FS: 00007f984f9b2700(0000) GS:ffff88089f380000(0000) knlGS:0000000000000000
>> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> > CR2: ffff880870187ed8 CR3: 00000008645f8000 CR4: 00000000001426e0
>> > Stack:
>> > ffffffff810cc83d 00000000632c3d28 0000000000000000 ffffffff81ea03c0
>> > 0000000000000046 0000000000000003 0000000000000000 0000000000000000
>> > ffff8808632c3d80 ffffffff810cca44 ffff88087af63800 0000000000000286
>> > Call Trace:
>> > [<ffffffff810cc83d>] ? __wake_up_common+0x4d/0x80
>> > [<ffffffff810cca44>] __wake_up+0x34/0x50
>> > [<ffffffff815d99e3>] __vga_put+0x73/0xd0
>> > [<ffffffff815d9db4>] vga_put+0x54/0x80
>> > [<ffffffff8169d042>] vfio_pci_vga_rw+0x1d2/0x220
>> > [<ffffffff8169a7f3>] vfio_pci_rw+0x33/0x60
>> > [<ffffffff8169abf7>] vfio_pci_write+0x17/0x20
>> > [<ffffffff816966a6>] vfio_device_fops_write+0x26/0x30
>> > [<ffffffff811a4b23>] __vfs_write+0x23/0xe0
>> > [<ffffffff811a4a53>] ? __vfs_read+0x23/0xd0
>> > [<ffffffff811b6e35>] ? do_vfs_ioctl+0x2b5/0x490
>> > [<ffffffff811a5194>] vfs_write+0xa4/0x190
>> > [<ffffffff811a5fa6>] SyS_pwrite64+0x66/0xa0
>> > [<ffffffff819a17d7>] entry_SYSCALL_64_fastpath+0x12/0x6a
>> > Code: 88 ff ff e0 7e 18 70 08 88 ff ff 00 8c 57 76 08 88 ff ff 20 7f 18 70 08 88 ff ff 08 7f 18 70 08 88 ff ff 94 51 1a 81 ff ff ff ff <09> 00 00 00 00 00 00 00 01 8c 57 76 08 88 ff ff 00 8c 57 76 08
>> > RIP [<ffff880870187ed8>] 0xffff880870187ed8
>> > RSP <ffff8808632c3d08>
>> > CR2: ffff880870187ed8
>> >
>> > The patch fixes the crash, but doesn't help with getting GPU in guest
>> > working again.
>> >
>> > Any ideas?
>> >
>> > ---
>> > drivers/gpu/vga/vgaarb.c | 6 ++++--
>> > 1 file changed, 4 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
>> > index 3166e4bc4eb6..9abcaa53bd25 100644
>> > --- a/drivers/gpu/vga/vgaarb.c
>> > +++ b/drivers/gpu/vga/vgaarb.c
>> > @@ -395,8 +395,10 @@ int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
>> > set_current_state(interruptible ?
>> > TASK_INTERRUPTIBLE :
>> > TASK_UNINTERRUPTIBLE);
>> > - if (signal_pending(current)) {
>> > - rc = -EINTR;
>> > + if (interruptible && signal_pending(current)) {
>> > + __set_current_state(TASK_RUNNING);
>> > + remove_wait_queue(&vga_wait_queue, &wait);
>> > + rc = -ERESTARTSYS;
>> > break;
>>
>> All 3 points are valid, and the patch looks good to me:
>>
>> Reviewed-by: David Herrmann <[email protected]>
>>
>> However, there seems to be a race between vga_lock and putting the
>> thread asleep.
>
> I'm not sure I understand the race you're talking about.
> Could you elaborate?
Normal wake-up race. You have to check the condition you wait for
*after* linking your wait-queue and setting your thread-state. In the
current code, if the wake-up happens between spin_unlock_irqrestore()
and add_wait_queue(), you will never get woken up.
Thanks
David
On Mon, Dec 14, 2015 at 11:20:00AM +0100, David Herrmann wrote:
> Hi
>
> On Mon, Dec 14, 2015 at 9:19 AM, Kirill A. Shutemov
> <[email protected]> wrote:
> > On Thu, Dec 10, 2015 at 11:28:58AM +0100, David Herrmann wrote:
> >> Hi
> >>
> >> On Mon, Nov 30, 2015 at 3:17 AM, Kirill A. Shutemov
> >> <[email protected]> wrote:
> >> > There are few defects in vga_get() related to signal hadning:
> >> >
> >> > - we shouldn't check for pending signals for TASK_UNINTERRUPTIBLE
> >> > case;
> >> >
> >> > - if we found pending signal we must remove ourself from wait queue
> >> > and change task state back to running;
> >> >
> >> > - -ERESTARTSYS is more appropriate, I guess.
> >> >
> >> > Signed-off-by: Kirill A. Shutemov <[email protected]>
> >> > ---
> >> >
> >> > Alex, I try to get KVM with VGA passthrough working properly. I have i915
> >> > (HD 4600) on the host and GTX 580 for the guest. The guest GPU is not
> >> > capabale of EFI, so I have to use x-vga=on. It's kinda work with your
> >> > patch for i915.enable_hd_vgaarb=1. But guest refuse to initialize the GPU
> >> > after KVM was not shut down correctly, resulting in host crash like this:
> >> >
> >> > BUG: unable to handle kernel paging request at ffff880870187ed8
> >> > IP: [<ffff880870187ed8>] 0xffff880870187ed8
> >> > PGD 2129067 PUD 80000008400001e3
> >> > Oops: 0011 [#1] PREEMPT SMP
> >> > Modules linked in: iwlmvm iwlwifi
> >> > CPU: 6 PID: 3983 Comm: qemu-system-x86 Not tainted 4.3.0-gentoo #6
> >> > Hardware name: Gigabyte Technology Co., Ltd. Z87X-UD7 TH/Z87X-UD7 TH-CF, BIOS F5a 06/12/2014
> >> > task: ffff88087a910000 ti: ffff8808632c0000 task.ti: ffff8808632c0000
> >> > RIP: 0010:[<ffff880870187ed8>] [<ffff880870187ed8>] 0xffff880870187ed8
> >> > RSP: 0018:ffff8808632c3d08 EFLAGS: 00010006
> >> > RAX: ffff880870187db0 RBX: 0000000070187f58 RCX: 0000000000000000
> >> > RDX: 0000000000000000 RSI: 0000000000000003 RDI: ffff880870187db0
> >> > RBP: ffff8808632c3d48 R08: 0000000000000000 R09: 0000000000000000
> >> > R10: 00000000000103c0 R11: 0000000000000293 R12: ffffffff81ea03c8
> >> > R13: ffffffff8104c7cb R14: 0000000000000000 R15: 0000000000000003
> >> > FS: 00007f984f9b2700(0000) GS:ffff88089f380000(0000) knlGS:0000000000000000
> >> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> > CR2: ffff880870187ed8 CR3: 00000008645f8000 CR4: 00000000001426e0
> >> > Stack:
> >> > ffffffff810cc83d 00000000632c3d28 0000000000000000 ffffffff81ea03c0
> >> > 0000000000000046 0000000000000003 0000000000000000 0000000000000000
> >> > ffff8808632c3d80 ffffffff810cca44 ffff88087af63800 0000000000000286
> >> > Call Trace:
> >> > [<ffffffff810cc83d>] ? __wake_up_common+0x4d/0x80
> >> > [<ffffffff810cca44>] __wake_up+0x34/0x50
> >> > [<ffffffff815d99e3>] __vga_put+0x73/0xd0
> >> > [<ffffffff815d9db4>] vga_put+0x54/0x80
> >> > [<ffffffff8169d042>] vfio_pci_vga_rw+0x1d2/0x220
> >> > [<ffffffff8169a7f3>] vfio_pci_rw+0x33/0x60
> >> > [<ffffffff8169abf7>] vfio_pci_write+0x17/0x20
> >> > [<ffffffff816966a6>] vfio_device_fops_write+0x26/0x30
> >> > [<ffffffff811a4b23>] __vfs_write+0x23/0xe0
> >> > [<ffffffff811a4a53>] ? __vfs_read+0x23/0xd0
> >> > [<ffffffff811b6e35>] ? do_vfs_ioctl+0x2b5/0x490
> >> > [<ffffffff811a5194>] vfs_write+0xa4/0x190
> >> > [<ffffffff811a5fa6>] SyS_pwrite64+0x66/0xa0
> >> > [<ffffffff819a17d7>] entry_SYSCALL_64_fastpath+0x12/0x6a
> >> > Code: 88 ff ff e0 7e 18 70 08 88 ff ff 00 8c 57 76 08 88 ff ff 20 7f 18 70 08 88 ff ff 08 7f 18 70 08 88 ff ff 94 51 1a 81 ff ff ff ff <09> 00 00 00 00 00 00 00 01 8c 57 76 08 88 ff ff 00 8c 57 76 08
> >> > RIP [<ffff880870187ed8>] 0xffff880870187ed8
> >> > RSP <ffff8808632c3d08>
> >> > CR2: ffff880870187ed8
> >> >
> >> > The patch fixes the crash, but doesn't help with getting GPU in guest
> >> > working again.
> >> >
> >> > Any ideas?
> >> >
> >> > ---
> >> > drivers/gpu/vga/vgaarb.c | 6 ++++--
> >> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >> >
> >> > diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> >> > index 3166e4bc4eb6..9abcaa53bd25 100644
> >> > --- a/drivers/gpu/vga/vgaarb.c
> >> > +++ b/drivers/gpu/vga/vgaarb.c
> >> > @@ -395,8 +395,10 @@ int vga_get(struct pci_dev *pdev, unsigned int rsrc, int interruptible)
> >> > set_current_state(interruptible ?
> >> > TASK_INTERRUPTIBLE :
> >> > TASK_UNINTERRUPTIBLE);
> >> > - if (signal_pending(current)) {
> >> > - rc = -EINTR;
> >> > + if (interruptible && signal_pending(current)) {
> >> > + __set_current_state(TASK_RUNNING);
> >> > + remove_wait_queue(&vga_wait_queue, &wait);
> >> > + rc = -ERESTARTSYS;
> >> > break;
> >>
> >> All 3 points are valid, and the patch looks good to me:
> >>
> >> Reviewed-by: David Herrmann <[email protected]>
> >>
> >> However, there seems to be a race between vga_lock and putting the
> >> thread asleep.
> >
> > I'm not sure I understand the race you're talking about.
> > Could you elaborate?
>
> Normal wake-up race. You have to check the condition you wait for
> *after* linking your wait-queue and setting your thread-state. In the
> current code, if the wake-up happens between spin_unlock_irqrestore()
> and add_wait_queue(), you will never get woken up.
Ah, I see. Your patch looks good to me to fix the issue.
--
Kirill A. Shutemov