From ef91f0f32abf158ee3d8bb2ef28075a070e4c905 Mon Sep 17 00:00:00 2001 From: Shijie Luo via Kernel Date: Sat, 29 Feb 2020 01:32:23 -0500 Subject: [PATCH] ext4: add cond_resched() to __ext4_find_entry() mainline inclusion from mainline-v5.6-rc3 commit 9424ef56e13a1f14c57ea161eed3ecfdc7b2770e category: bugfix bugzilla: 31127 CVE: NA ------------------------------------------------- We tested a soft lockup problem in linux 4.19 which could also be found in linux 5.x. When dir inode takes up a large number of blocks, and if the directory is growing when we are searching, it's possible the restart branch could be called many times, and the do while loop could hold cpu a long time. Here is the call trace in linux 4.19. [ 473.756186] Call trace: [ 473.756196] dump_backtrace+0x0/0x198 [ 473.756199] show_stack+0x24/0x30 [ 473.756205] dump_stack+0xa4/0xcc [ 473.756210] watchdog_timer_fn+0x300/0x3e8 [ 473.756215] __hrtimer_run_queues+0x114/0x358 [ 473.756217] hrtimer_interrupt+0x104/0x2d8 [ 473.756222] arch_timer_handler_virt+0x38/0x58 [ 473.756226] handle_percpu_devid_irq+0x90/0x248 [ 473.756231] generic_handle_irq+0x34/0x50 [ 473.756234] __handle_domain_irq+0x68/0xc0 [ 473.756236] gic_handle_irq+0x6c/0x150 [ 473.756238] el1_irq+0xb8/0x140 [ 473.756286] ext4_es_lookup_extent+0xdc/0x258 [ext4] [ 473.756310] ext4_map_blocks+0x64/0x5c0 [ext4] [ 473.756333] ext4_getblk+0x6c/0x1d0 [ext4] [ 473.756356] ext4_bread_batch+0x7c/0x1f8 [ext4] [ 473.756379] ext4_find_entry+0x124/0x3f8 [ext4] [ 473.756402] ext4_lookup+0x8c/0x258 [ext4] [ 473.756407] __lookup_hash+0x8c/0xe8 [ 473.756411] filename_create+0xa0/0x170 [ 473.756413] do_mkdirat+0x6c/0x140 [ 473.756415] __arm64_sys_mkdirat+0x28/0x38 [ 473.756419] el0_svc_common+0x78/0x130 [ 473.756421] el0_svc_handler+0x38/0x78 [ 473.756423] el0_svc+0x8/0xc [ 485.755156] watchdog: BUG: soft lockup - CPU#2 stuck for 22s! [tmp:5149] Add cond_resched() to avoid soft lockup and to provide a better system responding. Link: https://lore.kernel.org/r/20200215080206.13293-1-luoshijie1@huawei.com Signed-off-by: Shijie Luo Signed-off-by: Theodore Ts'o Reviewed-by: Jan Kara Cc: stable@kernel.org Reviewed-by: zhangyi (F) Signed-off-by: Yang Yingliang --- fs/ext4/namei.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index 40cca4ca863b..d70d2391c8cb 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -1431,6 +1431,7 @@ static struct buffer_head * ext4_find_entry (struct inode *dir, /* * We deal with the read-ahead logic here. */ + cond_resched(); if (ra_ptr >= ra_max) { /* Refill the readahead buffer */ ra_ptr = 0; -- GitLab