• Luis R. Rodriguez's avatar
    kmod: add test driver to stress test the module loader · d9c6a72d
    Luis R. Rodriguez authored
    This adds a new stress test driver for kmod: the kernel module loader.
    The new stress test driver, test_kmod, is only enabled as a module right
    now.  It should be possible to load this as built-in and load tests
    early (refer to the force_init_test module parameter), however since a
    lot of test can get a system out of memory fast we leave this disabled
    for now.
    
    Using a system with 1024 MiB of RAM can *easily* get your kernel OOM
    fast with this test driver.
    
    The test_kmod driver exposes API knobs for us to fine tune simple
    request_module() and get_fs_type() calls.  Since these API calls only
    allow each one parameter a test driver for these is rather simple.
    Other factors that can help out test driver though are the number of
    calls we issue and knowing current limitations of each.  This exposes
    configuration as much as possible through userspace to be able to build
    tests directly from userspace.
    
    Since it allows multiple misc devices its will eventually (once we add a
    knob to let us create new devices at will) also be possible to perform
    more tests in parallel, provided you have enough memory.
    
    We only enable tests we know work as of right now.
    
    Demo screenshots:
    
     # tools/testing/selftests/kmod/kmod.sh
    kmod_test_0001_driver: OK! - loading kmod test
    kmod_test_0001_driver: OK! - Return value: 256 (MODULE_NOT_FOUND), expected MODULE_NOT_FOUND
    kmod_test_0001_fs: OK! - loading kmod test
    kmod_test_0001_fs: OK! - Return value: -22 (-EINVAL), expected -EINVAL
    kmod_test_0002_driver: OK! - loading kmod test
    kmod_test_0002_driver: OK! - Return value: 256 (MODULE_NOT_FOUND), expected MODULE_NOT_FOUND
    kmod_test_0002_fs: OK! - loading kmod test
    kmod_test_0002_fs: OK! - Return value: -22 (-EINVAL), expected -EINVAL
    kmod_test_0003: OK! - loading kmod test
    kmod_test_0003: OK! - Return value: 0 (SUCCESS), expected SUCCESS
    kmod_test_0004: OK! - loading kmod test
    kmod_test_0004: OK! - Return value: 0 (SUCCESS), expected SUCCESS
    kmod_test_0005: OK! - loading kmod test
    kmod_test_0005: OK! - Return value: 0 (SUCCESS), expected SUCCESS
    kmod_test_0006: OK! - loading kmod test
    kmod_test_0006: OK! - Return value: 0 (SUCCESS), expected SUCCESS
    kmod_test_0005: OK! - loading kmod test
    kmod_test_0005: OK! - Return value: 0 (SUCCESS), expected SUCCESS
    kmod_test_0006: OK! - loading kmod test
    kmod_test_0006: OK! - Return value: 0 (SUCCESS), expected SUCCESS
    XXX: add test restult for 0007
    Test completed
    
    You can also request for specific tests:
    
     # tools/testing/selftests/kmod/kmod.sh -t 0001
    kmod_test_0001_driver: OK! - loading kmod test
    kmod_test_0001_driver: OK! - Return value: 256 (MODULE_NOT_FOUND), expected MODULE_NOT_FOUND
    kmod_test_0001_fs: OK! - loading kmod test
    kmod_test_0001_fs: OK! - Return value: -22 (-EINVAL), expected -EINVAL
    Test completed
    
    Lastly, the current available number of tests:
    
     # tools/testing/selftests/kmod/kmod.sh --help
    Usage: tools/testing/selftests/kmod/kmod.sh [ -t <4-number-digit> ]
    Valid tests: 0001-0009
    
    0001 - Simple test - 1 thread  for empty string
    0002 - Simple test - 1 thread  for modules/filesystems that do not exist
    0003 - Simple test - 1 thread  for get_fs_type() only
    0004 - Simple test - 2 threads for get_fs_type() only
    0005 - multithreaded tests with default setup - request_module() only
    0006 - multithreaded tests with default setup - get_fs_type() only
    0007 - multithreaded tests with default setup test request_module() and get_fs_type()
    0008 - multithreaded - push kmod_concurrent over max_modprobes for request_module()
    0009 - multithreaded - push kmod_concurrent over max_modprobes for get_fs_type()
    
    The following test cases currently fail, as such they are not currently
    enabled by default:
    
     # tools/testing/selftests/kmod/kmod.sh -t 0008
     # tools/testing/selftests/kmod/kmod.sh -t 0009
    
    To be sure to run them as intended please unload both of the modules:
    
      o test_module
      o xfs
    
    And ensure they are not loaded on your system prior to testing them.  If
    you use these paritions for your rootfs you can change the default test
    driver used for get_fs_type() by exporting it into your environment.  For
    example of other test defaults you can override refer to kmod.sh
    allow_user_defaults().
    
    Behind the scenes this is how we fine tune at a test case prior to
    hitting a trigger to run it:
    
    cat /sys/devices/virtual/misc/test_kmod0/config
    echo -n "2" > /sys/devices/virtual/misc/test_kmod0/config_test_case
    echo -n "ext4" > /sys/devices/virtual/misc/test_kmod0/config_test_fs
    echo -n "80" > /sys/devices/virtual/misc/test_kmod0/config_num_threads
    cat /sys/devices/virtual/misc/test_kmod0/config
    echo -n "1" > /sys/devices/virtual/misc/test_kmod0/config_num_threads
    
    Finally to trigger:
    
    echo -n "1" > /sys/devices/virtual/misc/test_kmod0/trigger_config
    
    The kmod.sh script uses the above constructs to build different test cases.
    
    A bit of interpretation of the current failures follows, first two
    premises:
    
    a) When request_module() is used userspace figures out an optimized
       version of module order for us.  Once it finds the modules it needs, as
       per depmod symbol dep map, it will finit_module() the respective
       modules which are needed for the original request_module() request.
    
    b) We have an optimization in place whereby if a kernel uses
       request_module() on a module already loaded we never bother userspace
       as the module already is loaded.  This is all handled by kernel/kmod.c.
    
    A few things to consider to help identify root causes of issues:
    
    0) kmod 19 has a broken heuristic for modules being assumed to be
       built-in to your kernel and will return 0 even though request_module()
       failed.  Upgrade to a newer version of kmod.
    
    1) A get_fs_type() call for "xfs" will request_module() for "fs-xfs",
       not for "xfs".  The optimization in kernel described in b) fails to
       catch if we have a lot of consecutive get_fs_type() calls.  The reason
       is the optimization in place does not look for aliases.  This means two
       consecutive get_fs_type() calls will bump kmod_concurrent, whereas
       request_module() will not.
    
    This one explanation why test case 0009 fails at least once for
    get_fs_type().
    
    2) If a module fails to load --- for whatever reason (kmod_concurrent
       limit reached, file not yet present due to rootfs switch, out of
       memory) we have a period of time during which module request for the
       same name either with request_module() or get_fs_type() will *also*
       fail to load even if the file for the module is ready.
    
    This explains why *multiple* NULLs are possible on test 0009.
    
    3) finit_module() consumes quite a bit of memory.
    
    4) Filesystems typically also have more dependent modules than other
       modules, its important to note though that even though a get_fs_type()
       call does not incur additional kmod_concurrent bumps, since userspace
       loads dependencies it finds it needs via finit_module_fd(), it *will*
       take much more memory to load a module with a lot of dependencies.
    
    Because of 3) and 4) we will easily run into out of memory failures with
    certain tests.  For instance test 0006 fails on qemu with 1024 MiB of RAM.
    It panics a box after reaping all userspace processes and still not
    having enough memory to reap.
    
    [arnd@arndb.de: add dependencies for test module]
      Link: http://lkml.kernel.org/r/20170630154834.3689272-1-arnd@arndb.de
    Link: http://lkml.kernel.org/r/20170628223155.26472-3-mcgrof@kernel.orgSigned-off-by: default avatarLuis R. Rodriguez <mcgrof@kernel.org>
    Cc: Jessica Yu <jeyu@redhat.com>
    Cc: Shuah Khan <shuah@kernel.org>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Michal Marek <mmarek@suse.com>
    Cc: Petr Mladek <pmladek@suse.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    d9c6a72d
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