From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f171.google.com (mail-pf0-f171.google.com [209.85.192.171]) by kanga.kvack.org (Postfix) with ESMTP id AB722828F3 for ; Mon, 8 Feb 2016 05:22:15 -0500 (EST) Received: by mail-pf0-f171.google.com with SMTP id e127so12251481pfe.3 for ; Mon, 08 Feb 2016 02:22:15 -0800 (PST) Received: from mx2.parallels.com (mx2.parallels.com. [199.115.105.18]) by mx.google.com with ESMTPS id 10si44185202pfk.172.2016.02.08.02.22.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 08 Feb 2016 02:22:14 -0800 (PST) Subject: Re: [PATCHv8] mm: slab: free kmem_cache_node after destroy sysfs file References: <1454923907-25901-1-git-send-email-dsafonov@virtuozzo.com> <20160208095831.GB30053@esperanza> From: Dmitry Safonov Message-ID: <56B86C4F.7030604@virtuozzo.com> Date: Mon, 8 Feb 2016 13:22:07 +0300 MIME-Version: 1.0 In-Reply-To: <20160208095831.GB30053@esperanza> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vladimir Davydov Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com, Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim On 02/08/2016 12:58 PM, Vladimir Davydov wrote: > On Mon, Feb 08, 2016 at 12:31:47PM +0300, Dmitry Safonov wrote: >> With enabled slub_debug alloc_calls_show will try to track location and >> user of slab object on each online node, kmem_cache_node structure and >> cpu_cache/cpu_slub shouldn't be freed till there is the last reference >> to sysfs file. >> >> Fixes the following panic: >> [43963.463055] BUG: unable to handle kernel >> [43963.463090] NULL pointer dereference at 0000000000000020 >> [43963.463146] IP: [] list_locations+0x169/0x4e0 >> [43963.463185] PGD 257304067 PUD 438456067 PMD 0 >> [43963.463220] Oops: 0000 [#1] SMP >> [43963.463850] CPU: 3 PID: 973074 Comm: cat ve: 0 Not tainted 3.10.0-229.7.2.ovz.9.30-00007-japdoll-dirty #2 9.30 >> [43963.463913] Hardware name: DEPO Computers To Be Filled By O.E.M./H67DE3, BIOS L1.60c 07/14/2011 >> [43963.463976] task: ffff88042a5dc5b0 ti: ffff88037f8d8000 task.ti: ffff88037f8d8000 >> [43963.464036] RIP: 0010:[] [] list_locations+0x169/0x4e0 >> [43963.464725] Call Trace: >> [43963.464756] [] alloc_calls_show+0x1d/0x30 >> [43963.464793] [] slab_attr_show+0x1b/0x30 >> [43963.464829] [] sysfs_read_file+0x9a/0x1a0 >> [43963.464865] [] vfs_read+0x9c/0x170 >> [43963.464900] [] SyS_read+0x58/0xb0 >> [43963.464936] [] system_call_fastpath+0x16/0x1b >> [43963.464970] Code: 5e 07 12 00 b9 00 04 00 00 3d 00 04 00 00 0f 4f c1 3d 00 04 00 00 89 45 b0 0f 84 c3 00 00 00 48 63 45 b0 49 8b 9c c4 f8 00 00 00 <48> 8b 43 20 48 85 c0 74 b6 48 89 df e8 46 37 44 00 48 8b 53 10 >> [43963.465119] RIP [] list_locations+0x169/0x4e0 >> [43963.465155] RSP >> [43963.465185] CR2: 0000000000000020 >> >> Separated __kmem_cache_release from __kmem_cache_shutdown which now >> called on slab_kmem_cache_release (after the last reference to sysfs >> file object has dropped). >> Reintroduced locking in free_partial as sysfs file might access cache's >> partial list after shutdowning - partiall revert of the >> commit 69cb8e6b7c2982 ("slub: free slabs without holding locks") >> >> Cc: Christoph Lameter >> Cc: Pekka Enberg >> Cc: David Rientjes >> Cc: Joonsoo Kim >> Suggested-by: Vladimir Davydov >> Signed-off-by: Dmitry Safonov > The patch looks good to me now, thanks. > > Acked-by: Vladimir Davydov Thank you for helping me with that patch. Will resend v9 with your ack and nits. > > Two minor nits below: > > ... >> /* >> * Attempt to free all partial slabs on a node. >> - * This is called from kmem_cache_close(). We must be the last thread >> - * using the cache and therefore we do not need to lock anymore. >> + * This is called from __kmem_cache_shutdown(). We must take list_lock >> + * because sysfs file might still access partial list after the shutdowning. >> */ >> static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n) >> { >> + unsigned long flags; >> struct page *page, *h; >> >> + spin_lock_irqsave(&n->list_lock, flags); > Nit: this function is never called with irqs disabled, so > spin_lock_irq() would be enough. We could add BUG_ON(irqs_disabled()) > just to be sure. > >> list_for_each_entry_safe(page, h, &n->partial, lru) { >> if (!page->inuse) { >> __remove_partial(n, page); > Nit: __remove_partial() (with leading underscores) was introduced solely > to avoid lockdep warning here (see 1e4dd9461fabf). Since we now take > list_lock, we can use remove_partial() (w/o underscores) and hence zap > __remove_partial(). > > Thanks, > Vladimir > >> discard_slab(s, page); >> } else { >> list_slab_objects(s, page, >> - "Objects remaining in %s on kmem_cache_close()"); >> + "Objects remaining in %s on __kmem_cache_shutdown()"); >> } >> } >> + spin_unlock_irqrestore(&n->list_lock, flags); >> } -- Regards, Dmitry Safonov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org