On Tue, Mar 08, 2016 at 11:08:05PM -0800, Davidlohr Bueso wrote:
> For the case of rtmutex torturing we will randomly call into the
> boost() handler, including upon module exiting when the tasks are
> deboosted before stopping. In such cases the task may or may not have
> already been boosted, and therefore the NULL being explicitly passed
> can occur anywhere. Currently we only assume that the task will is
> at a higher prio, and in consequence, dereference a nil pointer.
>
> This patch fixes the case of a rmmod locktorture exploding while
> pounding on the rtmutex lock (partial trace):
>
> [83317.452251] task: ffff88081026cf80 ti: ffff880816120000 task.ti:
> ffff880816120000
> [83317.452258] RIP: 0010:[<ffffffffa05c6185>] [<ffffffffa05c6185>]
> torture_random+0x5/0x60 [torture]
> [83317.452261] RSP: 0018:ffff880816123eb0 EFLAGS: 00010206
> [83317.452264] RAX: ffff88081026cf80 RBX: ffff880816bfa630 RCX:
> 0000000000160d1b
> [83317.452267] RDX: 0000000000000000 RSI: 0000000000000202 RDI:
> 0000000000000000
> [83317.452269] RBP: ffff88081026cf80 R08: 000000000000001f R09:
> ffff88017c20ca80
> [83317.452271] R10: 0000000000000000 R11: 000000000048c316 R12:
> ffffffffa05d1840
> [83317.452273] R13: 0000000000000000 R14: 0000000000000000 R15:
> 0000000000000000
> [83317.452275] FS: 0000000000000000(0000) GS:ffff88203f880000(0000)
> knlGS:0000000000000000
> [83317.452277] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [83317.452279] CR2: 0000000000000008 CR3: 0000000001c0a000 CR4:
> 00000000000406e0
> [83317.452281] Stack:
> [83317.452288] ffffffffa05d141d ffff880816bfa630 ffffffffa05d1922
> ffff88081e70c2c0
> [83317.452295] ffff880816bfa630 ffffffff81095fed 0000000000000000
> ffffffff8107bf60
> [83317.452297] ffff880816bfa630 ffffffff00000000 ffff880800000000
> ffff880816123f08
> [83317.452297] Call Trace:
> [83317.452309] [<ffffffffa05d141d>] torture_rtmutex_boost+0x1d/0x90
> [locktorture]
> [83317.452315] [<ffffffffa05d1922>] lock_torture_writer+0xe2/0x170
> [locktorture]
> [83317.452321] [<ffffffff81095fed>] kthread+0xbd/0xe0
> [83317.452325] [<ffffffff815cf40f>] ret_from_fork+0x3f/0x70
>
> This patch ensures that if the random state pointer is not nil and current
> is not boosted, then do nothing.
>
> Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
Queued for 4.7, thank you!!!
(If you need it earlier, please let me know.)
Thanx, Paul
> ---
> kernel/locking/locktorture.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> index 8ef1919d63b2..9e9c5f454f5c 100644
> --- a/kernel/locking/locktorture.c
> +++ b/kernel/locking/locktorture.c
> @@ -394,12 +394,12 @@ static void torture_rtmutex_boost(struct
> torture_random_state *trsp)
>
> if (!rt_task(current)) {
> /*
> - * (1) Boost priority once every ~50k operations. When the
> + * Boost priority once every ~50k operations. When the
> * task tries to take the lock, the rtmutex it will account
> * for the new priority, and do any corresponding pi-dance.
> */
> - if (!(torture_random(trsp) %
> - (cxt.nrealwriters_stress * factor))) {
> + if (trsp && !(torture_random(trsp) %
> + (cxt.nrealwriters_stress * factor))) {
> policy = SCHED_FIFO;
> param.sched_priority = MAX_RT_PRIO - 1;
> } else /* common case, do nothing */
> --
> 2.1.4
>
