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From: Nikolay Borisov <nborisov@suse.com>
To: linux-btrfs@vger.kernel.org
Cc: Nikolay Borisov <nborisov@suse.com>
Subject: [PATCH] btrfs: Relinquish CPUs in btrfs_compare_trees
Date: Wed,  4 Sep 2019 19:33:58 +0300	[thread overview]
Message-ID: <20190904163358.11591-1-nborisov@suse.com> (raw)

When doing any form of incremental send the parent and the child trees
need to be compared via btrfs_compare_trees. This  can result in long
loop chains without ever relinquishing the CPU. This causes softlockup
detector to trigger when comparing trees with a lot of items. Example
report:

watchdog: BUG: soft lockup - CPU#0 stuck for 24s! [snapperd:16153]
CPU: 0 PID: 16153 Comm: snapperd Not tainted 5.2.9-1-default #1 openSUSE Tumbleweed (unreleased)
Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
pstate: 40000005 (nZcv daif -PAN -UAO)
pc : __ll_sc_arch_atomic_sub_return+0x14/0x20
lr : btrfs_release_extent_buffer_pages+0xe0/0x1e8 [btrfs]
sp : ffff00001273b7e0
Call trace:
 __ll_sc_arch_atomic_sub_return+0x14/0x20
 release_extent_buffer+0xdc/0x120 [btrfs]
 free_extent_buffer.part.0+0xb0/0x118 [btrfs]
 free_extent_buffer+0x24/0x30 [btrfs]
 btrfs_release_path+0x4c/0xa0 [btrfs]
 btrfs_free_path.part.0+0x20/0x40 [btrfs]
 btrfs_free_path+0x24/0x30 [btrfs]
 get_inode_info+0xa8/0xf8 [btrfs]
 finish_inode_if_needed+0xe0/0x6d8 [btrfs]
 changed_cb+0x9c/0x410 [btrfs]
 btrfs_compare_trees+0x284/0x648 [btrfs]
 send_subvol+0x33c/0x520 [btrfs]
 btrfs_ioctl_send+0x8a0/0xaf0 [btrfs]
 btrfs_ioctl+0x199c/0x2288 [btrfs]
 do_vfs_ioctl+0x4b0/0x820
 ksys_ioctl+0x84/0xb8
 __arm64_sys_ioctl+0x28/0x38
 el0_svc_common.constprop.0+0x7c/0x188
 el0_svc_handler+0x34/0x90
 el0_svc+0x8/0xc

Fix this by adding a call to cond_resched at the beginning of the main
loop in btrfs_compare_trees.

Fixes: 7069830a9e38 ("Btrfs: add btrfs_compare_trees function")
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 fs/btrfs/send.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index f856d6ca3771..f3215028235c 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -6757,6 +6757,7 @@ static int btrfs_compare_trees(struct btrfs_root *left_root,
 	advance_left = advance_right = 0;
 
 	while (1) {
+		cond_resched();
 		if (advance_left && !left_end_reached) {
 			ret = tree_advance(left_path, &left_level,
 					left_root_level,
-- 
2.17.1


             reply	other threads:[~2019-09-04 16:34 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-04 16:33 Nikolay Borisov [this message]
2019-09-05  8:37 ` [PATCH] btrfs: Relinquish CPUs in btrfs_compare_trees Johannes Thumshirn
2019-09-05 15:31 ` David Sterba

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