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SubjectPossible race in loop.ko
While searching for races in Linux kernel I've come across
drivers/block/loop.ko module. Here is the question that I came up with
while analyzing results. Lines are given using the info from Linux v4.12.

In loop_init function additional initialization happens after a
successful call to misc_register() (loop.c: line 1961). Consider the
following case:

Thread 1: Thread 2:
misc_register() loop_control_ioctl
part_shift = 0 -> loop_add
if (max_part > 0) { alloc_disk(1 << part_shift)
part_shift =
<greater than 0>

In this case alloc_disk() will be called with 1 as a parameter although
part_shift should have been greater than 0. Maybe it would be better to
move the call to a misc_register() function a bit further down (at least
so it could be after the part_shift initialization)?

Thank you for your time.

-- Anton Volkov
Linux Verification Center, ISPRAS

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