RFC: FROMLIST: cgroup: reduce read locked section of cgroup_threadgroup_rwsem during fork
cgroup_threadgroup_rwsem is acquired in read mode during process exit
and fork. It is also grabbed in write mode during
__cgroups_proc_write(). I've recently run into a scenario with lots
of memory pressure and OOM and I am beginning to see
systemd
__switch_to+0x1f8/0x350
__schedule+0x30c/0x990
schedule+0x48/0xc0
percpu_down_write+0x114/0x170
__cgroup_procs_write.isra.12+0xb8/0x3c0
cgroup_file_write+0x74/0x1a0
kernfs_fop_write+0x188/0x200
__vfs_write+0x6c/0xe0
vfs_write+0xc0/0x230
SyS_write+0x6c/0x110
system_call+0x38/0xb4
This thread is waiting on the reader of cgroup_threadgroup_rwsem to
exit. The reader itself is under memory pressure and has gone into
reclaim after fork. There are times the reader also ends up waiting on
oom_lock as well.
__switch_to+0x1f8/0x350
__schedule+0x30c/0x990
schedule+0x48/0xc0
jbd2_log_wait_commit+0xd4/0x180
ext4_evict_inode+0x88/0x5c0
evict+0xf8/0x2a0
dispose_list+0x50/0x80
prune_icache_sb+0x6c/0x90
super_cache_scan+0x190/0x210
shrink_slab.part.15+0x22c/0x4c0
shrink_zone+0x288/0x3c0
do_try_to_free_pages+0x1dc/0x590
try_to_free_pages+0xdc/0x260
__alloc_pages_nodemask+0x72c/0xc90
alloc_pages_current+0xb4/0x1a0
page_table_alloc+0xc0/0x170
__pte_alloc+0x58/0x1f0
copy_page_range+0x4ec/0x950
copy_process.isra.5+0x15a0/0x1870
_do_fork+0xa8/0x4b0
ppc_clone+0x8/0xc
In the meanwhile, all processes exiting/forking are blocked almost
stalling the system.
This patch moves the threadgroup_change_begin from before
cgroup_fork() to just before cgroup_canfork(). There is no nee to
worry about threadgroup changes till the task is actually added to the
threadgroup. This avoids having to call reclaim with
cgroup_threadgroup_rwsem held.
tj: Subject and description edits.
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Acked-by: Zefan Li <lizefan@huawei.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Tejun Heo <tj@kernel.org>
[jstultz: Cherry-picked from:
git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git 568ac888215c7f]
Change-Id: Ie8ece84fb613cf6a7b08cea1468473a8df2b9661
Signed-off-by: John Stultz <john.stultz@linaro.org>
Git-commit: e91f1799ff
Git-repo: https://android.googlesource.com/kernel/common/+/android-4.4
Signed-off-by: Omprakash Dhyade <odhyade@codeaurora.org>
This commit is contained in:
parent
00eaad05be
commit
35f2961082
1 changed files with 2 additions and 2 deletions
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@ -1375,7 +1375,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
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p->real_start_time = ktime_get_boot_ns();
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p->io_context = NULL;
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p->audit_context = NULL;
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threadgroup_change_begin(current);
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cgroup_fork(p);
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#ifdef CONFIG_NUMA
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p->mempolicy = mpol_dup(p->mempolicy);
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@ -1527,6 +1526,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
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INIT_LIST_HEAD(&p->thread_group);
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p->task_works = NULL;
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threadgroup_change_begin(current);
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/*
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* Ensure that the cgroup subsystem policies allow the new process to be
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* forked. It should be noted the the new process's css_set can be changed
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@ -1627,6 +1627,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
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bad_fork_cancel_cgroup:
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cgroup_cancel_fork(p, cgrp_ss_priv);
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bad_fork_free_pid:
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threadgroup_change_end(current);
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if (pid != &init_struct_pid)
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free_pid(pid);
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bad_fork_cleanup_io:
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@ -1657,7 +1658,6 @@ bad_fork_cleanup_policy:
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mpol_put(p->mempolicy);
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bad_fork_cleanup_threadgroup_lock:
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#endif
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threadgroup_change_end(current);
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delayacct_tsk_free(p);
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bad_fork_cleanup_count:
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atomic_dec(&p->cred->user->processes);
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