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 15:36:08 +0800 |
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On Fri, 2022-09-02 at 08:58 +0200, Greg Kroah-Hartman wrote: > On Fri, Sep 02, 2022 at 02:40:59PM +0800, Kuyo Chang wrote: > > 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. > > Eeeek, nice find! I've been adding this pattern: > debugfs_remove(debugfs_lookup(...)); > all over the place, and as you point out, that's wrong! > > It's as if I didn't even read the documentation I wrote. > > {sigh} > > Ok, as this is going to be a very common pattern, how about we > create: > debugfs_lookup_and_remove() > function that does the above logic all in one place and then we don't > have to put that logic everywhere in the kernel. My goal is for > users > of debugfs to never have to worry about anything about 'struct > dentry' > at all, and I really failed that goal here in a major way. > > I can work on that this afternoon after I get some other things done, > unless you want to do it now? > > Again, very nice find, thank you for this. >
Thanks for your kindly support ! Please help to add debugfs_lookup_and_remove() and then we can use this api to fix this denrty leak issue.
> greg k-h
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