linux-kernel - Re: [interval_tree_test_init] BUG: soft lockup

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Date:   Wed, 8 Nov 2017 15:26:30 +0800
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [interval_tree_test_init] BUG: soft lockup - CPU#0 stuck for
 23s! [swapper/0:1]

On Tue, Nov 07, 2017 at 08:58:14AM -0800, Davidlohr Bueso wrote:
>On Tue, 07 Nov 2017, Fengguang Wu wrote:
>
>>[  265.102312] xz_dec_test: module loaded
>>[  265.111774] xz_dec_test: Create a device node with 'mknod xz_dec_test c 246 0' and write .xz files to it.
>>[  265.160320] atomic64_test: passed for x86-64 platform with CX8 and with SSE
>>[  265.181966] glob: 64 self-tests passed, 0 failed
>>[  265.196996] interval tree insert/remove
>>[  292.348094] watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [swapper/0:1]
>>[  292.348094] irq event stamp: 6190340
>>[  292.396418] hardirqs last  enabled at (6190339): [<ffffffff81fb006b>] restore_regs_and_iret+0x0/0x1d
>>[  292.396418] hardirqs last disabled at (6190340): [<ffffffff81fb0cb8>] apic_timer_interrupt+0x98/0xb0
>>[  292.396418] softirqs last  enabled at (6182242): [<ffffffff81fb2942>] __do_softirq+0x382/0x3f7
>>[  292.396418] softirqs last disabled at (6182235): [<ffffffff810b6696>] irq_exit+0x51/0x7b
>>[  292.396418] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.14.0-rc8 #40
>>[  292.396418] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
>>[  292.396418] task: ffff880072bf4040 task.stack: ffffc9000031c000
>>[  292.396418] RIP: 0010:interval_tree_insert+0x4c/0xd4
>
>That would be:
>
>     for (i = 0; i < perf_loops; i++) {
>	 for (j = 0; j < nnodes; j++)
>		interval_tree_insert(nodes + j, &root);
>	 for (j = 0; j < nnodes; j++)
>		interval_tree_remove(nodes + j, &root);
>     }
>
>Which if you are using the default params would end up doing insert() 10 million times.
>How about decrementing perf_loops, it's pretty high.

It works! Thank you!

Tested-by: Fengguang Wu <fengguang.wu@...el.com>

Fengguang

>diff --git a/lib/interval_tree_test.c b/lib/interval_tree_test.c
>index 0e343fd29570..1dbdf3704247 100644
>--- a/lib/interval_tree_test.c
>+++ b/lib/interval_tree_test.c
>@@ -11,7 +11,7 @@
>        MODULE_PARM_DESC(name, msg);
>
> __param(int, nnodes, 100, "Number of nodes in the interval tree");
>-__param(int, perf_loops, 100000, "Number of iterations modifying the tree");
>+__param(int, perf_loops, 1000, "Number of iterations modifying the tree");
>
> __param(int, nsearches, 100, "Number of searches to the interval tree");
> __param(int, search_loops, 10000, "Number of iterations searching the tree");
>
>If that works I guess we'd have to limit the max values for such parameters
>to avoid soft lockups. The same applies to your rbtree test report.
>
>Thanks,
>Davidlohr
>