Messages in this thread | | | Subject | Re: [PATCH 1/1] sched/debug: fix dentry leak in update_sched_domain_debugfs | From | Kuyo Chang <> | Date | Fri, 2 Sep 2022 14:40:59 +0800 |
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On Fri, 2022-09-02 at 07:26 +0200, Greg Kroah-Hartman wrote: > On Fri, Sep 02, 2022 at 11:15:15AM +0800, Kuyo Chang wrote: > > From: kuyo chang <kuyo.chang@mediatek.com> > > > > [Syndrome] > > Lowmemorykiller triggered while doing hotplug stress test as below > > cmd: > > echo [0/1] > /sys/devices/system/cpu/cpu${index}/online > > > > Rootcause: > > Call trace of the slab owner & usage as below after hotplug stress > > test(4hr). > > There exists dentry leak at update_sched_domain_debugfs. > > > > Total size : 322000KB > > <prep_new_page+44>: > > <get_page_from_freelist+672>: > > <__alloc_pages+304>: > > <allocate_slab+144>: > > <___slab_alloc+404>: > > <__slab_alloc+60>: > > <kmem_cache_alloc+1204>: > > <alloc_inode+100>: > > <new_inode+40>: > > <__debugfs_create_file+172>: > > <update_sched_domain_debugfs+824>: > > <partition_sched_domains_locked+1292>: > > <rebuild_sched_domains_locked+576>: > > <cpuset_hotplug_workfn+1052>: > > <process_one_work+584>: > > <worker_thread+1008>: > > > > [Solution] > > Provided by Major Chen <major.chen@samsung.com> as below link. > > https://lore.kernel.org/lkml/20220711030341epcms5p173848e98b13c09eb2fcdf2fd7287526a@epcms5p1/ > > update_sched_domain_debugfs() uses debugfs_lookup() to find wanted > > dentry(which has > > been created by debugfs_create_dir() before), but not call dput() > > to return this dentry > > back. This result in dentry leak even debugfs_remove() is called. > > > > [Test result] > > Using below commands to check inode_cache & dentry leak. > > cat /proc/slabinfo | grep -w inode_cache > > cat /proc/slabinfo | grep -w dentry > > > > With the patch, the inode_cache & dentry stays consistent > > so the lowmemorykiller will not triggered anymore. > > > > Fixes: 8a99b6833c88 ("sched: Move SCHED_DEBUG sysctl to debugfs") > > > > Signed-off-by: Major Chen <major.chen@samsung.com> > > Signed-off-by: kuyo chang <kuyo.chang@mediatek.com> > > Tested-by: kuyo chang <kuyo.chang@mediatek.com> > > > > --- > > kernel/sched/debug.c | 7 +++++-- > > 1 file changed, 5 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c > > index bb3d63bdf4ae..4ffea2dc01da 100644 > > --- a/kernel/sched/debug.c > > +++ b/kernel/sched/debug.c > > @@ -412,11 +412,14 @@ void update_sched_domain_debugfs(void) > > > > for_each_cpu(cpu, sd_sysctl_cpus) { > > struct sched_domain *sd; > > - struct dentry *d_cpu; > > + struct dentry *d_cpu, *d_lookup; > > char buf[32]; > > > > snprintf(buf, sizeof(buf), "cpu%d", cpu); > > - debugfs_remove(debugfs_lookup(buf, sd_dentry)); > > + d_lookup = debugfs_lookup(buf, sd_dentry); > > + debugfs_remove(d_lookup); > > + if (!IS_ERR_OR_NULL(d_lookup)) > > + dput(d_lookup); > > That's odd, and means that something else is removing this file right > after we looked it up? Is there a missing lock here that should be > used > instead? > > thanks, > > greg k-h
While doing cpu hotlug, the cpu_active_mask is changed, so it need to update_sched_domain_debugfs.
The original design is to recreate sd_dentry, so it doing debugfs_remove and then debugfs_create_dir. However, by debugfs_lookup function usage. The returned dentry must be passed to dput() when it is no longer needed to avoid dentry leak.
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