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author | Tejun Heo <tj@kernel.org> | 2019-05-29 13:46:25 -0700 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-06-19 08:18:00 +0200 |
commit | c3b85bda41f0a8c00b7492cbc9042b612dad2162 (patch) | |
tree | 68a377789787d8f4c88d6dba7d7f6e4056b9f79d /include/linux | |
parent | e599bfe54305231eb8381453f2bf1641fd4e62c7 (diff) | |
download | linux-stable-c3b85bda41f0a8c00b7492cbc9042b612dad2162.tar.gz linux-stable-c3b85bda41f0a8c00b7492cbc9042b612dad2162.tar.bz2 linux-stable-c3b85bda41f0a8c00b7492cbc9042b612dad2162.zip |
cgroup: Use css_tryget() instead of css_tryget_online() in task_get_css()
commit 18fa84a2db0e15b02baa5d94bdb5bd509175d2f6 upstream.
A PF_EXITING task can stay associated with an offline css. If such
task calls task_get_css(), it can get stuck indefinitely. This can be
triggered by BSD process accounting which writes to a file with
PF_EXITING set when racing against memcg disable as in the backtrace
at the end.
After this change, task_get_css() may return a css which was already
offline when the function was called. None of the existing users are
affected by this change.
INFO: rcu_sched self-detected stall on CPU
INFO: rcu_sched detected stalls on CPUs/tasks:
...
NMI backtrace for cpu 0
...
Call Trace:
<IRQ>
dump_stack+0x46/0x68
nmi_cpu_backtrace.cold.2+0x13/0x57
nmi_trigger_cpumask_backtrace+0xba/0xca
rcu_dump_cpu_stacks+0x9e/0xce
rcu_check_callbacks.cold.74+0x2af/0x433
update_process_times+0x28/0x60
tick_sched_timer+0x34/0x70
__hrtimer_run_queues+0xee/0x250
hrtimer_interrupt+0xf4/0x210
smp_apic_timer_interrupt+0x56/0x110
apic_timer_interrupt+0xf/0x20
</IRQ>
RIP: 0010:balance_dirty_pages_ratelimited+0x28f/0x3d0
...
btrfs_file_write_iter+0x31b/0x563
__vfs_write+0xfa/0x140
__kernel_write+0x4f/0x100
do_acct_process+0x495/0x580
acct_process+0xb9/0xdb
do_exit+0x748/0xa00
do_group_exit+0x3a/0xa0
get_signal+0x254/0x560
do_signal+0x23/0x5c0
exit_to_usermode_loop+0x5d/0xa0
prepare_exit_to_usermode+0x53/0x80
retint_user+0x8/0x8
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v4.2+
Fixes: ec438699a9ae ("cgroup, block: implement task_get_css() and use it in bio_associate_current()")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux')
-rw-r--r-- | include/linux/cgroup.h | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index ca51b2c15bcc..8937d48a5389 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -485,7 +485,7 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task, * * Find the css for the (@task, @subsys_id) combination, increment a * reference on and return it. This function is guaranteed to return a - * valid css. + * valid css. The returned css may already have been offlined. */ static inline struct cgroup_subsys_state * task_get_css(struct task_struct *task, int subsys_id) @@ -495,7 +495,13 @@ task_get_css(struct task_struct *task, int subsys_id) rcu_read_lock(); while (true) { css = task_css(task, subsys_id); - if (likely(css_tryget_online(css))) + /* + * Can't use css_tryget_online() here. A task which has + * PF_EXITING set may stay associated with an offline css. + * If such task calls this function, css_tryget_online() + * will keep failing. + */ + if (likely(css_tryget(css))) break; cpu_relax(); } |