From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Brauner Subject: Re: [PATCH v2] usercopy: Avoid soft lockups in test_check_nonzero_user() Date: Wed, 16 Oct 2019 14:50:26 +0200 Message-ID: <20191016125025.ktxe55l4doirbxbe@wittgenstein> References: <20191011022447.24249-1-mpe@ellerman.id.au> <20191016122732.13467-1-mpe@ellerman.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <20191016122732.13467-1-mpe@ellerman.id.au> Sender: linux-kernel-owner@vger.kernel.org To: Michael Ellerman Cc: cyphar@cyphar.com, mingo@redhat.com, peterz@infradead.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, christian@brauner.io, keescook@chromium.org, linux@rasmusvillemoes.dk, viro@zeniv.linux.org.uk, torvalds@linux-foundation.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-api@vger.kernel.org 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 > Signed-off-by: Michael Ellerman Thanks! Acked-by: Christian Brauner