Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753177AbZKPQXz (ORCPT ); Mon, 16 Nov 2009 11:23:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752810AbZKPQXy (ORCPT ); Mon, 16 Nov 2009 11:23:54 -0500 Received: from smtp-outbound-1.vmware.com ([65.115.85.69]:53536 "EHLO smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752790AbZKPQXy (ORCPT ); Mon, 16 Nov 2009 11:23:54 -0500 Message-ID: <4B017C93.3010807@vmware.com> Date: Mon, 16 Nov 2009 17:23:47 +0100 From: Thomas Hellstrom User-Agent: Thunderbird 2.0.0.23 (X11/20090822) MIME-Version: 1.0 To: Dave Airlie CC: Jerome Glisse , "dri-devel@lists.sf.net" , LKML , Chris Wilson Subject: Re: [PATCH 2/2] drm: mm always protect change to unused_nodes with unused_lock spinlock References: <1258142218-2070-1-git-send-email-jglisse@redhat.com> <21d7e9970911151542n49f15a9dn6481d0bc2bdfbc45@mail.gmail.com> In-Reply-To: <21d7e9970911151542n49f15a9dn6481d0bc2bdfbc45@mail.gmail.com> Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3707 Lines: 93 Dave Airlie wrote: > On Sat, Nov 14, 2009 at 5:56 AM, Jerome Glisse wrote: > >> unused_nodes modification needs to be protected by unused_lock spinlock. >> Here is an example of an usage where there is no such protection without >> this patch. >> >> Process 1: 1-drm_mm_pre_get(this function modify unused_nodes list) >> 2-spin_lock(spinlock protecting mm struct) >> 3-drm_mm_put_block(this function might modify unused_nodes >> list but doesn't protect modification with unused_lock) >> 4-spin_unlock(spinlock protecting mm struct) >> Process2: 1-drm_mm_pre_get(this function modify unused_nodes list) >> At this point Process1 & Process2 might both be doing modification to >> unused_nodes list. This patch add unused_lock protection into >> drm_mm_put_block to avoid such issue. >> > > Have we got a bug number or reproducer for this? > > I've cc'ed Thomas and Chris who were last ppl to touch drm_mm.c for some > sort of acks. > > Dave. > > >> Signed-off-by: Jerome Glisse >> --- >> drivers/gpu/drm/drm_mm.c | 9 +++++++++ >> 1 files changed, 9 insertions(+), 0 deletions(-) >> >> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c >> index c861d80..97dc5a4 100644 >> --- a/drivers/gpu/drm/drm_mm.c >> +++ b/drivers/gpu/drm/drm_mm.c >> @@ -103,6 +103,11 @@ static struct drm_mm_node *drm_mm_kmalloc(struct drm_mm *mm, int atomic) >> return child; >> } >> >> +/* drm_mm_pre_get() - pre allocate drm_mm_node structure >> + * drm_mm: memory manager struct we are pre-allocating for >> + * >> + * Returns 0 on success or -ENOMEM if allocation fails. >> + */ >> int drm_mm_pre_get(struct drm_mm *mm) >> { >> struct drm_mm_node *node; >> @@ -253,12 +258,14 @@ void drm_mm_put_block(struct drm_mm_node *cur) >> prev_node->size += next_node->size; >> list_del(&next_node->ml_entry); >> list_del(&next_node->fl_entry); >> + spin_lock(&mm->unused_lock); >> if (mm->num_unused < MM_UNUSED_TARGET) { >> list_add(&next_node->fl_entry, >> &mm->unused_nodes); >> ++mm->num_unused; >> } else >> kfree(next_node); >> + spin_unlock(&mm->unused_lock); >> } else { >> next_node->size += cur->size; >> next_node->start = cur->start; >> @@ -271,11 +278,13 @@ void drm_mm_put_block(struct drm_mm_node *cur) >> list_add(&cur->fl_entry, &mm->fl_entry); >> } else { >> list_del(&cur->ml_entry); >> + spin_lock(&mm->unused_lock); >> if (mm->num_unused < MM_UNUSED_TARGET) { >> list_add(&cur->fl_entry, &mm->unused_nodes); >> ++mm->num_unused; >> } else >> kfree(cur); >> + spin_unlock(&mm->unused_lock); >> } >> } >> >> -- >> 1.6.5.2 >> >> >> Hmm. Ouch. The patch looks correct, although I'm not 100% sure it's OK to kfree() within a spinlocked region? Perhaps better to take it out. /Thomas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/