From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f170.google.com (mail-pf0-f170.google.com [209.85.192.170]) by kanga.kvack.org (Postfix) with ESMTP id 1E165828F3 for ; Mon, 8 Feb 2016 04:58:45 -0500 (EST) Received: by mail-pf0-f170.google.com with SMTP id c10so40554877pfc.2 for ; Mon, 08 Feb 2016 01:58:45 -0800 (PST) Received: from mx2.parallels.com (mx2.parallels.com. [199.115.105.18]) by mx.google.com with ESMTPS id vw1si45491228pab.74.2016.02.08.01.58.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 08 Feb 2016 01:58:44 -0800 (PST) Date: Mon, 8 Feb 2016 12:58:31 +0300 From: Vladimir Davydov Subject: Re: [PATCHv8] mm: slab: free kmem_cache_node after destroy sysfs file Message-ID: <20160208095831.GB30053@esperanza> References: <1454923907-25901-1-git-send-email-dsafonov@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1454923907-25901-1-git-send-email-dsafonov@virtuozzo.com> Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Safonov 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 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 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); > } -- 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