Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932375AbbLNKUV (ORCPT ); Mon, 14 Dec 2015 05:20:21 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:36063 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932286AbbLNKUB (ORCPT ); Mon, 14 Dec 2015 05:20:01 -0500 MIME-Version: 1.0 In-Reply-To: <20151214081956.GA29540@node.shutemov.name> References: <1448849851-26061-1-git-send-email-kirill@shutemov.name> <20151214081956.GA29540@node.shutemov.name> Date: Mon, 14 Dec 2015 11:20:00 +0100 Message-ID: Subject: Re: [PATCH] vgaarb: fix signal handling in vga_get() From: David Herrmann To: "Kirill A. Shutemov" Cc: Dave Airlie , Daniel Vetter , Alex Williamson , David Airlie , kvm@vger.kernel.org, "dri-devel@lists.freedesktop.org" , linux-kernel , vfio-users@redhat.com Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5410 Lines: 117 Hi On Mon, Dec 14, 2015 at 9:19 AM, Kirill A. Shutemov 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 >> 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 >> > --- >> > >> > 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: [] 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:[] [] 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: >> > [] ? __wake_up_common+0x4d/0x80 >> > [] __wake_up+0x34/0x50 >> > [] __vga_put+0x73/0xd0 >> > [] vga_put+0x54/0x80 >> > [] vfio_pci_vga_rw+0x1d2/0x220 >> > [] vfio_pci_rw+0x33/0x60 >> > [] vfio_pci_write+0x17/0x20 >> > [] vfio_device_fops_write+0x26/0x30 >> > [] __vfs_write+0x23/0xe0 >> > [] ? __vfs_read+0x23/0xd0 >> > [] ? do_vfs_ioctl+0x2b5/0x490 >> > [] vfs_write+0xa4/0x190 >> > [] SyS_pwrite64+0x66/0xa0 >> > [] 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 [] 0xffff880870187ed8 >> > RSP >> > 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 >> >> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/