When vm.dirtytime_expire_seconds is set to 0, wakeup_dirtytime_writeback() schedules delayed work with a delay of 0, causing immediate execution. The function then reschedules itself with 0 delay again, creating an infinite busy loop that causes 100% kworker CPU usage.
Fix by: - Only scheduling delayed work in wakeup_dirtytime_writeback() when dirtytime_expire_interval is non-zero - Cancelling the delayed work in dirtytime_interval_handler() when the interval is set to 0 - Adding a guard in start_dirtytime_writeback() for defensive coding
Tested by booting kernel in QEMU with virtme-ng: - Before fix: kworker CPU spikes to ~73% - After fix: CPU remains at normal levels - Setting interval back to non-zero correctly resumes writeback
Fixes: a2f4870697a5 ("fs: make sure the timestamps for lazytime inodes eventually get written") Cc: stable@vger.kernel.org Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220227 Signed-off-by: Laveesh Bansal laveeshb@laveeshbansal.com --- fs/fs-writeback.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 6800886c4d10..cd21c74cd0e5 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -2492,7 +2492,8 @@ static void wakeup_dirtytime_writeback(struct work_struct *w) wb_wakeup(wb); } rcu_read_unlock(); - schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); + if (dirtytime_expire_interval) + schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); }
static int dirtytime_interval_handler(const struct ctl_table *table, int write, @@ -2501,8 +2502,12 @@ static int dirtytime_interval_handler(const struct ctl_table *table, int write, int ret;
ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); - if (ret == 0 && write) - mod_delayed_work(system_percpu_wq, &dirtytime_work, 0); + if (ret == 0 && write) { + if (dirtytime_expire_interval) + mod_delayed_work(system_percpu_wq, &dirtytime_work, 0); + else + cancel_delayed_work_sync(&dirtytime_work); + } return ret; }
@@ -2519,7 +2524,8 @@ static const struct ctl_table vm_fs_writeback_table[] = {
static int __init start_dirtytime_writeback(void) { - schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); + if (dirtytime_expire_interval) + schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ); register_sysctl_init("vm", vm_fs_writeback_table); return 0; }