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Syzkaller reported the following bug:
sysfs: cannot create duplicate filename '/devices/iommufd_mock4'
Call Trace:
sysfs_warn_dup+0x71/0x90
sysfs_create_dir_ns+0x1ee/0x260
? sysfs_create_mount_point+0x80/0x80
? spin_bug+0x1d0/0x1d0
? do_raw_spin_unlock+0x54/0x220
kobject_add_internal+0x221/0x970
kobject_add+0x11c/0x1e0
? lockdep_hardirqs_on_prepare+0x273/0x3e0
? kset_create_and_add+0x160/0x160
? kobject_put+0x5d/0x390
? bus_get_dev_root+0x4a/0x60
? kobject_put+0x5d/0x390
device_add+0x1d5/0x1550
? __fw_devlink_link_to_consumers.isra.0+0x1f0/0x1f0
? __init_waitqueue_head+0xcb/0x150
iommufd_test+0x462/0x3b60
? lock_release+0x1fe/0x640
? __might_fault+0x117/0x170
? reacquire_held_locks+0x4b0/0x4b0
? iommufd_selftest_destroy+0xd0/0xd0
? __might_fault+0xbe/0x170
iommufd_fops_ioctl+0x256/0x350
? iommufd_option+0x180/0x180
? __lock_acquire+0x1755/0x45f0
__x64_sys_ioctl+0xa13/0x1640
The bug is triggered when Syzkaller created multiple mock devices but
didn't destroy them in the same sequence, messing up the mock_dev_num
counter. Replace the atomic with an mock_dev_ida.
Cc: stable@vger.kernel.org
Fixes: 23a1b46f15 ("iommufd/selftest: Make the mock iommu driver into a real driver")
Link: https://lore.kernel.org/r/5af41d5af6d5c013cc51de01427abb8141b3587e.1708636627.git.nicolinc@nvidia.com
Reported-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Linux kernel
============
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There are various text files in the Documentation/ subdirectory,
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Please read the Documentation/process/changes.rst file, as it contains the
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