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![Michael Ellerman](https://secure.gravatar.com/avatar/d080344ef56b855bc10918cad51d85da.jpg?s=96&d=mm)
Michael Ellerman committed f418dddffc8
usercopy: Avoid soft lockups in test_check_nonzero_user() 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: f5a1a536fa14 ("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>