From: Shijie Luo luoshijie1@huawei.com
commit 9424ef56e13a1f14c57ea161eed3ecfdc7b2770e upstream.
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 luoshijie1@huawei.com Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Jan Kara jack@suse.cz Cc: stable@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/namei.c | 1 + 1 file changed, 1 insertion(+)
--- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -1507,6 +1507,7 @@ restart: /* * We deal with the read-ahead logic here. */ + cond_resched(); if (ra_ptr >= ra_max) { /* Refill the readahead buffer */ ra_ptr = 0;