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Thu, 12 Nov 2020 18:31:57 -0800 Received: from MTKMBS01N1.mediatek.inc (172.21.101.68) by MTKMBS62N2.mediatek.inc (172.29.193.42) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 12 Nov 2020 18:31:56 -0800 Received: from mtkcas10.mediatek.inc (172.21.101.39) by mtkmbs01n1.mediatek.inc (172.21.101.68) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 13 Nov 2020 10:31:53 +0800 Received: from [172.21.84.99] (172.21.84.99) by mtkcas10.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Fri, 13 Nov 2020 10:31:54 +0800 Message-ID: <1605234714.30076.18.camel@mtksdccf07> Subject: Re: [PATCH 1/1] kasan: fix object remain in offline per-cpu quarantine From: Kuan-Ying Lee To: Dmitry Vyukov Date: Fri, 13 Nov 2020 10:31:54 +0800 In-Reply-To: References: <1605162252-23886-1-git-send-email-Kuan-Ying.Lee@mediatek.com> <1605162252-23886-2-git-send-email-Kuan-Ying.Lee@mediatek.com> X-Mailer: Evolution 3.2.3-0ubuntu6 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201112_213209_497495_D4DEDF72 X-CRM114-Status: GOOD ( 46.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: wsd_upstream , nicholas.tang@mediatek.com, linux-mediatek@lists.infradead.org, LKML , kasan-dev , Linux-MM , Miles Chen , Alexander Potapenko , Matthias Brugger , Andrey Ryabinin , Andrew Morton , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 2020-11-12 at 09:39 +0100, Dmitry Vyukov wrote: > On Thu, Nov 12, 2020 at 7:25 AM Kuan-Ying Lee > wrote: > > > > We hit this issue in our internal test. > > When enabling generic kasan, a kfree()'d object is put into per-cpu > > quarantine first. If the cpu goes offline, object still remains in > > the per-cpu quarantine. If we call kmem_cache_destroy() now, slub > > will report "Objects remaining" error. > > > > [ 74.982625] ============================================================================= > > [ 74.983380] BUG test_module_slab (Not tainted): Objects remaining in test_module_slab on __kmem_cache_shutdown() > > [ 74.984145] ----------------------------------------------------------------------------- > > [ 74.984145] > > [ 74.984883] Disabling lock debugging due to kernel taint > > [ 74.985561] INFO: Slab 0x(____ptrval____) objects=34 used=1 fp=0x(____ptrval____) flags=0x2ffff00000010200 > > [ 74.986638] CPU: 3 PID: 176 Comm: cat Tainted: G B 5.10.0-rc1-00007-g4525c8781ec0-dirty #10 > > [ 74.987262] Hardware name: linux,dummy-virt (DT) > > [ 74.987606] Call trace: > > [ 74.987924] dump_backtrace+0x0/0x2b0 > > [ 74.988296] show_stack+0x18/0x68 > > [ 74.988698] dump_stack+0xfc/0x168 > > [ 74.989030] slab_err+0xac/0xd4 > > [ 74.989346] __kmem_cache_shutdown+0x1e4/0x3c8 > > [ 74.989779] kmem_cache_destroy+0x68/0x130 > > [ 74.990176] test_version_show+0x84/0xf0 > > [ 74.990679] module_attr_show+0x40/0x60 > > [ 74.991218] sysfs_kf_seq_show+0x128/0x1c0 > > [ 74.991656] kernfs_seq_show+0xa0/0xb8 > > [ 74.992059] seq_read+0x1f0/0x7e8 > > [ 74.992415] kernfs_fop_read+0x70/0x338 > > [ 74.993051] vfs_read+0xe4/0x250 > > [ 74.993498] ksys_read+0xc8/0x180 > > [ 74.993825] __arm64_sys_read+0x44/0x58 > > [ 74.994203] el0_svc_common.constprop.0+0xac/0x228 > > [ 74.994708] do_el0_svc+0x38/0xa0 > > [ 74.995088] el0_sync_handler+0x170/0x178 > > [ 74.995497] el0_sync+0x174/0x180 > > [ 74.996050] INFO: Object 0x(____ptrval____) @offset=15848 > > [ 74.996752] INFO: Allocated in test_version_show+0x98/0xf0 age=8188 cpu=6 pid=172 > > [ 75.000802] stack_trace_save+0x9c/0xd0 > > [ 75.002420] set_track+0x64/0xf0 > > [ 75.002770] alloc_debug_processing+0x104/0x1a0 > > [ 75.003171] ___slab_alloc+0x628/0x648 > > [ 75.004213] __slab_alloc.isra.0+0x2c/0x58 > > [ 75.004757] kmem_cache_alloc+0x560/0x588 > > [ 75.005376] test_version_show+0x98/0xf0 > > [ 75.005756] module_attr_show+0x40/0x60 > > [ 75.007035] sysfs_kf_seq_show+0x128/0x1c0 > > [ 75.007433] kernfs_seq_show+0xa0/0xb8 > > [ 75.007800] seq_read+0x1f0/0x7e8 > > [ 75.008128] kernfs_fop_read+0x70/0x338 > > [ 75.008507] vfs_read+0xe4/0x250 > > [ 75.008990] ksys_read+0xc8/0x180 > > [ 75.009462] __arm64_sys_read+0x44/0x58 > > [ 75.010085] el0_svc_common.constprop.0+0xac/0x228 > > [ 75.011006] kmem_cache_destroy test_module_slab: Slab cache still has objects > > > > Register a cpu hotplug function to remove all objects in the offline > > per-cpu quarantine when cpu is going offline. Set a per-cpu variable > > to indicate this cpu is offline. > > > > Signed-off-by: Kuan-Ying Lee > > --- > > mm/kasan/quarantine.c | 59 +++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 57 insertions(+), 2 deletions(-) > > > > diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c > > index 4c5375810449..67fb91ae2bd0 100644 > > --- a/mm/kasan/quarantine.c > > +++ b/mm/kasan/quarantine.c > > @@ -29,6 +29,7 @@ > > #include > > #include > > #include > > +#include > > > > #include "../slab.h" > > #include "kasan.h" > > @@ -97,6 +98,7 @@ static void qlist_move_all(struct qlist_head *from, struct qlist_head *to) > > * guarded by quarantine_lock. > > */ > > Hi Kuan-Ying, > > Thanks for fixing this. > > > static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine); > > +static DEFINE_PER_CPU(int, cpu_quarantine_offline); > > I think cpu_quarantine_offline is better be part of cpu_quarantine > because it logically is and we already obtain a pointer to > cpu_quarantine in quarantine_put, so it will also make the code a bit > shorter. > Ok. Got it. > > > /* Round-robin FIFO array of batches. */ > > static struct qlist_head global_quarantine[QUARANTINE_BATCHES]; > > @@ -176,6 +178,8 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache) > > unsigned long flags; > > struct qlist_head *q; > > struct qlist_head temp = QLIST_INIT; > > + int *offline; > > + struct qlist_head q_offline = QLIST_INIT; > > > > /* > > * Note: irq must be disabled until after we move the batch to the > > @@ -187,8 +191,16 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache) > > */ > > local_irq_save(flags); > > > > - q = this_cpu_ptr(&cpu_quarantine); > > - qlist_put(q, &info->quarantine_link, cache->size); > > + offline = this_cpu_ptr(&cpu_quarantine_offline); > > + if (*offline == 0) { > > + q = this_cpu_ptr(&cpu_quarantine); > > + qlist_put(q, &info->quarantine_link, cache->size); > > + } else { > > + qlist_put(&q_offline, &info->quarantine_link, cache->size); > > + qlist_free_all(&q_offline, cache); > > This looks like a convoluted way to call qlink_free. I think it will > be better to call qlink_free directly here. > > And why do we need this? Because CPU shutdown code can still free some > objects afterwards? > Yes, it is because IRQ can happen during CPU shutdown and free some objects into offline CPU quarantine. > > + local_irq_restore(flags); > > + return; > > You add both if/else and early return, this looks like unnecessary > code complication. It would be simpler with: > > if (*offline) { > qlink_free(...); > return; > } > ... all current per-cpu local ... > > Thank you for reminder. v2 Will do it. > > + } > > if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) { > > qlist_move_all(q, &temp); > > > > @@ -328,3 +340,46 @@ void quarantine_remove_cache(struct kmem_cache *cache) > > > > synchronize_srcu(&remove_cache_srcu); > > } > > + > > +static int kasan_cpu_online(unsigned int cpu) > > +{ > > + int *offline; > > + unsigned long flags; > > + > > + local_irq_save(flags); > > I assume this local_irq_save/restore is to prevent some warnings from > this_cpu_ptr. > But CPU online/offline callbacks should run without preemption already > (preempting/rescheduling on other CPUs does not make sense for them, > right?), so I would assume that is already at least preemption > disabled or something. Is there this_cpu_ptr variant that won't > produce warnings on its own in cpu online/offline callbacks? > This whole function could be a 1-liner: > this_cpu_ptr(&cpu_quarantine)->offline = true; > So I am trying to understand if we could avoid all this unnecessary danse. > Yes, it's unnecessary. v2 will fix it. > > > + offline = this_cpu_ptr(&cpu_quarantine_offline); > > + *offline = 0; > > + local_irq_restore(flags); > > + return 0; > > +} > > + > > +static int kasan_cpu_offline(unsigned int cpu) > > +{ > > + struct kmem_cache *s; > > + int *offline; > > + unsigned long flags; > > + > > + local_irq_save(flags); > > + offline = this_cpu_ptr(&cpu_quarantine_offline); > > + *offline = 1; > > + local_irq_restore(flags); > > + > > + mutex_lock(&slab_mutex); > > + list_for_each_entry(s, &slab_caches, list) { > > + per_cpu_remove_cache(s); > > + } > > + mutex_unlock(&slab_mutex); > > We just want to drop the whole per-cpu cache at once, right? I would > assume there should be a simpler way to do this all at once, rather > than doing this per-slab. > Yes. Is removing objects in per-cpu quarantine directly better? struct qlist_head *q; q = this_cpu_ptr(&cpu_quaratine); q->offline = true; qlist_free_all(q, NULL); > > + return 0; > > +} > > + > > +static int __init kasan_cpu_offline_quarantine_init(void) > > +{ > > + int ret = 0; > > + > > + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online", > > + kasan_cpu_online, kasan_cpu_offline); > > + if (ret) > > + pr_err("kasan offline cpu quarantine register failed [%d]\n", ret); > > + return ret; > > +} > > +late_initcall(kasan_cpu_offline_quarantine_init); > > -- > > 2.18.0 > > > > -- > > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com. > > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/1605162252-23886-2-git-send-email-Kuan-Ying.Lee%40mediatek.com. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel