Commit 1e77e130 authored Nov 01, 2019 by Rickard Möller Committed by Todd Kjos Nov 14, 2019

ANDROID: uid_sys_stats: avoid double accounting of dying threads



When a thread is being killed process_notifier() is called to record
the final accounting of the thread. But after that uid_cputime_show()
and add_uid_io_stats() can be called before the dying thread is
removed from the parent's thread_group resulting in double accounting.

This can cause the user and system time for a given UID to move
backwards in /proc/uid_cputime/show_uid_stat. That gives negative delta
times in KernelCpuUidUserSysTimeReader.readDeltaImpl() and it logs
an error:

"Negative user/sys time delta for UID=..."

One consequence of which was incorrectly calculated power consumptions
in BatteryStats.

With this change we avoid the double accounting by ignoring the thread
if it has the PF_EXITING flag set.

Bug: 144366911

Change-Id: I6b929e8f558cd81ce1c00481c8b550d24877aa2c
Signed-off-by: Rickard Möller <rickard.moller@sony.com>

parent 3a468438

drivers/misc/uid_sys_stats.c

+10 −3

Original line number	Diff line number	Diff line
		@@ -358,9 +358,12 @@ static int uid_cputime_show(struct seq_file m, void v)
		__func__, uid);
		return -ENOMEM;
		}
		/* avoid double accounting of dying threads */
		if (!(task->flags & PF_EXITING)) {
		task_cputime_adjusted(task, &utime, &stime);
		uid_entry->active_utime += utime;
		uid_entry->active_stime += stime;
		}
		} while_each_thread(temp, task);
		rcu_read_unlock();

		@@ -454,6 +457,10 @@ static void add_uid_io_stats(struct uid_entry *uid_entry,
		{
		struct io_stats *io_slot = &uid_entry->io[slot];

		/* avoid double accounting of dying threads */
		if (slot != UID_STATE_DEAD_TASKS && (task->flags & PF_EXITING))
		return;

		io_slot->read_bytes += task->ioac.read_bytes;
		io_slot->write_bytes += compute_write_bytes(task);
		io_slot->rchar += task->ioac.rchar;