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Date: Wed, 14 Aug 2013 09:29:29 +0200 From: Hans Verkuil <hverkuil@...all.nl> To: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com> Cc: Mauro Carvalho Chehab <mchehab@...hat.com>, Hans Verkuil <hans.verkuil@...co.com>, Tomasz Stanislawski <t.stanislaws@...sung.com>, Sakari Ailus <sakari.ailus@....fi>, Frank Schäfer <fschaefer.oss@...glemail.com>, linux-media@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] v4l2-dev: Fix race condition on __video_register_device On Tue 13 August 2013 17:04:06 Ricardo Ribalda Delgado wrote: > When 2 devices are registered at the same time, in Part 2 both will get > the same minor number, making Part6 crash, because it cannot create a > create a device with a duplicated minor: You would expect that such core code would be bug free by now, but this is indeed a race condition. Acked-by: Hans Verkuil <hans.verkuil@...co.com> Regards, Hans > > [ 7.157648] ------------[ cut here ]------------ > [ 7.157666] WARNING: at fs/sysfs/dir.c:530 sysfs_add_one+0xbd/0xe0() > [ 7.157669] sysfs: cannot create duplicate filename '/dev/char/81:1' > [ 7.157672] Modules linked in: qtec_xform(+) qt5023_video(+) videobuf2_vmalloc videobuf2_dma_sg videobuf2_memops videobuf2_core gpio_xilinx(+) qtec_white qtec_cmosis(+) qtec_pcie qt5023 > [ 7.157694] CPU: 0 PID: 120 Comm: systemd-udevd Not tainted 3.10.0-qtec-standard #8 > [ 7.157698] Hardware name: QTechnology QT5022/QT5022, BIOS PM_2.1.0.309 X64 05/23/2013 > [ 7.157702] 0000000000000009 ffff8801788358e8 ffffffff8176c487 ffff880178835928 > [ 7.157707] ffffffff8106f6f0 ffff880175759770 00000000ffffffef ffff880175759930 > [ 7.157712] ffff8801788359e8 ffff880178bff000 ffff880175759930 ffff880178835988 > [ 7.157718] Call Trace: > [ 7.157728] [<ffffffff8176c487>] dump_stack+0x19/0x1b > [ 7.157735] [<ffffffff8106f6f0>] warn_slowpath_common+0x70/0xa0 > [ 7.157740] [<ffffffff8106f7d6>] warn_slowpath_fmt+0x46/0x50 > [ 7.157746] [<ffffffff81324b35>] ? strlcat+0x65/0x90 > [ 7.157750] [<ffffffff811d516d>] sysfs_add_one+0xbd/0xe0 > [ 7.157755] [<ffffffff811d5c6b>] sysfs_do_create_link_sd+0xdb/0x200 > [ 7.157760] [<ffffffff811d5db1>] sysfs_create_link+0x21/0x40 > [ 7.157765] [<ffffffff813e277b>] device_add+0x21b/0x6d0 > [ 7.157772] [<ffffffff813f2985>] ? pm_runtime_init+0xe5/0xf0 > [ 7.157776] [<ffffffff813e2c4e>] device_register+0x1e/0x30 > [ 7.157782] [<ffffffff8153e8c3>] __video_register_device+0x313/0x610 > [ 7.157791] [<ffffffffa00957c5>] qtec_xform_probe+0x465/0x7a4 [qtec_xform] > [ 7.157797] [<ffffffff813e7b13>] platform_drv_probe+0x43/0x80 > [ 7.157802] [<ffffffff813e531a>] ? driver_sysfs_add+0x7a/0xb0 > [ 7.157807] [<ffffffff813e584b>] driver_probe_device+0x8b/0x3a0 > [ 7.157812] [<ffffffff813e5c0b>] __driver_attach+0xab/0xb0 > [ 7.157816] [<ffffffff813e5b60>] ? driver_probe_device+0x3a0/0x3a0 > [ 7.157820] [<ffffffff813e37fd>] bus_for_each_dev+0x5d/0xa0 > [ 7.157825] [<ffffffff813e529e>] driver_attach+0x1e/0x20 > [ 7.157829] [<ffffffff813e4d3e>] bus_add_driver+0x10e/0x280 > [ 7.157833] [<ffffffffa0099000>] ? 0xffffffffa0098fff > [ 7.157837] [<ffffffffa0099000>] ? 0xffffffffa0098fff > [ 7.157842] [<ffffffff813e6317>] driver_register+0x77/0x170 > [ 7.157848] [<ffffffff81151bcc>] ? __vunmap+0x9c/0x110 > [ 7.157852] [<ffffffffa0099000>] ? 0xffffffffa0098fff > [ 7.157857] [<ffffffff813e7236>] platform_driver_register+0x46/0x50 > [ 7.157863] [<ffffffffa0099010>] qtec_xform_plat_driver_init+0x10/0x12 [qtec_xform] > [ 7.157869] [<ffffffff810002ea>] do_one_initcall+0xea/0x1a0 > [ 7.157875] [<ffffffff810cf1f1>] load_module+0x1a91/0x2630 > [ 7.157880] [<ffffffff8133bee0>] ? ddebug_proc_show+0xe0/0xe0 > [ 7.157887] [<ffffffff817760f2>] ? page_fault+0x22/0x30 > [ 7.157892] [<ffffffff810cfe7a>] SyS_init_module+0xea/0x140 > [ 7.157898] [<ffffffff8177e5b9>] tracesys+0xd0/0xd5 > [ 7.157902] ---[ end trace 660cc3a65a4bf01b ]--- > [ 7.157939] __video_register_device: device_register failed > > Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com> > --- > drivers/media/v4l2-core/v4l2-dev.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c > index 5923c5d..3f75f99 100644 > --- a/drivers/media/v4l2-core/v4l2-dev.c > +++ b/drivers/media/v4l2-core/v4l2-dev.c > @@ -873,6 +873,7 @@ int __video_register_device(struct video_device *vdev, int type, int nr, > > /* Should not happen since we thought this minor was free */ > WARN_ON(video_device[vdev->minor] != NULL); > + video_device[vdev->minor] = vdev; > vdev->index = get_index(vdev); > mutex_unlock(&videodev_lock); > > @@ -936,9 +937,6 @@ int __video_register_device(struct video_device *vdev, int type, int nr, > #endif > /* Part 6: Activate this minor. The char device can now be used. */ > set_bit(V4L2_FL_REGISTERED, &vdev->flags); > - mutex_lock(&videodev_lock); > - video_device[vdev->minor] = vdev; > - mutex_unlock(&videodev_lock); > > return 0; > > @@ -946,6 +944,7 @@ cleanup: > mutex_lock(&videodev_lock); > if (vdev->cdev) > cdev_del(vdev->cdev); > + video_device[vdev->minor] = NULL; > devnode_clear(vdev); > mutex_unlock(&videodev_lock); > /* Mark this video device as never having been registered. */ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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