linux-kernel - Re: [PATCH v6 01/10] [hack] silence ttm fini WARNING

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Message-ID: <20210205073956.koeqlzh2suuzitgr@sirius.home.kraxel.org>
Date:   Fri, 5 Feb 2021 08:39:56 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Christian König <christian.koenig@....com>
Cc:     dri-devel@...ts.freedesktop.org, Huang Rui <ray.huang@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 01/10] [hack] silence ttm fini WARNING

On Thu, Feb 04, 2021 at 03:58:33PM +0100, Christian König wrote:
> ?
> 
> What's the background here?
> 
> Christian.
> 
> Am 04.02.21 um 15:57 schrieb Gerd Hoffmann:
> > kobject: '(null)' ((____ptrval____)): is not initialized, yet kobject_put() is being called.
> > WARNING: CPU: 0 PID: 209 at lib/kobject.c:750 kobject_put+0x3a/0x60
> > [ ... ]
> > Call Trace:
> >   ttm_device_fini+0x133/0x1b0 [ttm]
> >   qxl_ttm_fini+0x2f/0x40 [qxl]

Happens on driver removal.  Seen with both qxl and bochs (the later
using vram helpers).

Testcase: "drmtest --unbind" (https://git.kraxel.org/cgit/drminfo/).

static int try_unbind(int card)
{
    char path[256];
    char *device, *name;
    int fd;

    snprintf(path, sizeof(path), "/sys/class/drm/card%d/device", card);
    device = realpath(path, NULL);
    if (device == NULL) {
        fprintf(stderr, "%s: can't resolve sysfs device path\n", __func__);
        return -1;
    }

    snprintf(path, sizeof(path), "%s/driver/unbind", device);
    fd = open(path, O_WRONLY);
    if (fd < 0) {
        fprintf(stderr, "open %s: %s\n", path, strerror(errno));
        return -1;
    }

    name = strrchr(device, '/') + 1;
    write(fd, name, strlen(name));
    close(fd);
    return 0;
}

take care,
  Gerd