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f418dddffc
On a machine with a 64K PAGE_SIZE, the nested for loops in
test_check_nonzero_user() can lead to soft lockups, eg:
watchdog: BUG: soft lockup - CPU#4 stuck for 22s! [modprobe:611]
Modules linked in: test_user_copy(+) vmx_crypto gf128mul crc32c_vpmsum virtio_balloon ip_tables x_tables autofs4
CPU: 4 PID: 611 Comm: modprobe Tainted: G L 5.4.0-rc1-gcc-8.2.0-00001-gf5a1a536fa14-dirty #1151
...
NIP __might_sleep+0x20/0xc0
LR __might_fault+0x40/0x60
Call Trace:
check_zeroed_user+0x12c/0x200
test_user_copy_init+0x67c/0x1210 [test_user_copy]
do_one_initcall+0x60/0x340
do_init_module+0x7c/0x2f0
load_module+0x2d94/0x30e0
__do_sys_finit_module+0xc8/0x150
system_call+0x5c/0x68
Even with a 4K PAGE_SIZE the test takes multiple seconds. Instead
tweak it to only scan a 1024 byte region, but make it cross the
page boundary.
Fixes: f5a1a536fa ("lib: introduce copy_struct_from_user() helper")
Suggested-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Aleksa Sarai <cyphar@cyphar.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20191016122732.13467-1-mpe@ellerman.id.au
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.