mainlining shenanigans
39b3cab92d
The rcutorture module is used to run torture tests that validate RCU. rcutorture takes a variety of module parameters that configure the functionality of the test. Amongst these parameters are the types of synchronization mechanisms that the rcu_torture_writer and rcu_torture_fakewriter tasks may use, and the torture_type of the run which determines what read and sync operations are used by the various writer and reader tasks that run throughout the test. When the module is configured to only use sync types for which the specified torture_type does not implement the necessary operations, we can end up in a state where nsynctypes is 0. This is not an erroneous state, but it currently crashes the kernel with a #DE due to nsynctypes being used with a modulo operator in rcu_torture_fakewriter(). Here is an example of such a #DE: $ insmod ./rcutorture.ko gp_cond=1 gp_cond_exp=0 gp_exp=0 gp_poll_exp=0 gp_normal=0 gp_poll=0 gp_poll_exp=0 verbose=9999 torture_type=trivial ... [ 8536.525096] divide error: 0000 [#1] PREEMPT SMP PTI [ 8536.525101] CPU: 30 PID: 392138 Comm: rcu_torture_fak Kdump: loaded Tainted: G S 5.17.0-rc1-00179-gc8c42c80febd #24 [ 8536.525105] Hardware name: Quanta Twin Lakes MP/Twin Lakes Passive MP, BIOS F09_3A23 12/08/2020 [ 8536.525106] RIP: 0010:rcu_torture_fakewriter+0xf1/0x2d0 [rcutorture] [ 8536.525121] Code: 00 31 d2 8d 0c f5 00 00 00 00 48 63 c9 48 f7 f1 48 85 d2 0f 84 79 ff ff ff 48 89 e7 e8 78 78 01 00 48 63 0d 29 ca 00 00 31 d2 <48> f7 f1 8b 04 95 00 05 4e a0 83 f8 06 0f 84 ad 00 00 00 7f 1f 83 [ 8536.525124] RSP: 0018:ffffc9000777fef0 EFLAGS: 00010246 [ 8536.525127] RAX: 00000000223d006e RBX: cccccccccccccccd RCX: 0000000000000000 [ 8536.525130] RDX: 0000000000000000 RSI: ffffffff824315b9 RDI: ffffc9000777fef0 [ 8536.525132] RBP: ffffc9000487bb30 R08: 0000000000000002 R09: 000000000002a580 [ 8536.525134] R10: ffffffff82c5f920 R11: 0000000000000000 R12: ffff8881a2c35d00 [ 8536.525136] R13: ffff8881540c8d00 R14: ffffffffa04d39d0 R15: 0000000000000000 [ 8536.525137] FS: 0000000000000000(0000) GS:ffff88903ff80000(0000) knlGS:0000000000000000 [ 8536.525140] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 8536.525142] CR2: 00007f839f022000 CR3: 0000000002c0a006 CR4: 00000000007706e0 [ 8536.525144] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 8536.525145] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 8536.525147] PKRU: 55555554 [ 8536.525148] Call Trace: [ 8536.525150] <TASK> [ 8536.525153] kthread+0xe8/0x110 [ 8536.525161] ? kthread_complete_and_exit+0x20/0x20 [ 8536.525167] ret_from_fork+0x22/0x30 [ 8536.525174] </TASK> The solution is to gracefully handle the case of nsynctypes being 0 in rcu_torture_fakewriter() by not performing any work. This is already being done in rcu_torture_writer(), though there is a missing return on that path which will be fixed in a subsequent patch. Signed-off-by: David Vernet <void@manifault.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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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.