Re: [PATCH v2] usercopy: Avoid soft lockups in test_check_nonzero_user()
flat view
From: Christian Brauner <hidden>
Date: 2019-10-16 13:03:41
Also in:
lkml
On Wed, Oct 16, 2019 at 11:27:32PM +1100, Michael Ellerman wrote:
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 <redacted>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>With Aleksa's Reviewed-by I've picked this up: https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=copy_struct_from_user Thanks! Christian