From mboxrd@z Thu Jan 1 00:00:00 1970 From: mina86@mina86.com (Michal Nazarewicz) Date: Tue, 18 Feb 2014 18:44:08 +0100 Subject: [BUG] Circular locking dependency - DRM/CMA/MM/hotplug/... In-Reply-To: <53036D51.2070502@samsung.com> References: <20140211183543.GK26684@n2100.arm.linux.org.uk> <52FB9602.1000805@samsung.com> <20140212163317.GQ26684@n2100.arm.linux.org.uk> <53036D51.2070502@samsung.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > On 2014-02-12 17:33, Russell King - ARM Linux wrote: >> What if we did these changes: >> >> struct page *dma_alloc_from_contiguous(struct device *dev, int count, >> unsigned int align) >> { >> ... >> mutex_lock(&cma_mutex); >> ... >> for (;;) { >> pageno = bitmap_find_next_zero_area(cma->bitmap, cma->count, >> start, count, mask); >> if (pageno >= cma->count) >> break; >> >> pfn = cma->base_pfn + pageno; >> + bitmap_set(cma->bitmap, pageno, count); >> + mutex_unlock(&cma_mutex); >> ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA); >> + mutex_lock(&cma_mutex); >> if (ret == 0) { >> - bitmap_set(cma->bitmap, pageno, count); >> page = pfn_to_page(pfn); >> break; >> - } else if (ret != -EBUSY) { >> + } >> + bitmap_clear(cma->bitmap, pageno, count); >> + if (ret != -EBUSY) { >> break; >> } >> ... >> mutex_unlock(&cma_mutex); >> pr_debug("%s(): returned %p\n", __func__, page); >> return page; >> } Like Marek said, this will fail if two concurrent calls to alloc_contig_range are made such that they operate on the same pageblock (which is possible as the allocated regions do not need to be pageblock aligned). Another mutex could be added just for this one call, but as I understand this would not solve the problem. >> bool dma_release_from_contiguous(struct device *dev, struct page *pages, >> int count) >> { >> ... >> + free_contig_range(pfn, count); >> mutex_lock(&cma_mutex); >> bitmap_clear(cma->bitmap, pfn - cma->base_pfn, count); >> - free_contig_range(pfn, count); >> mutex_unlock(&cma_mutex); >> ... >> } This *should* be fine. Didn't test it. -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Micha? ?mina86? Nazarewicz (o o) ooo +------ooO--(_)--Ooo-- -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 835 bytes Desc: not available URL: From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Nazarewicz Subject: Re: [BUG] Circular locking dependency - DRM/CMA/MM/hotplug/... Date: Tue, 18 Feb 2014 18:44:08 +0100 Message-ID: References: <20140211183543.GK26684@n2100.arm.linux.org.uk> <52FB9602.1000805@samsung.com> <20140212163317.GQ26684@n2100.arm.linux.org.uk> <53036D51.2070502@samsung.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="=-=-=" Return-path: In-Reply-To: <53036D51.2070502@samsung.com> Sender: linux-kernel-owner@vger.kernel.org To: Marek Szyprowski , Russell King - ARM Linux Cc: linux-arm-kernel@lists.infradead.org, David Airlie , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org List-Id: dri-devel@lists.freedesktop.org --=-=-= Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable > On 2014-02-12 17:33, Russell King - ARM Linux wrote: >> What if we did these changes: >> >> struct page *dma_alloc_from_contiguous(struct device *dev, int count, >> unsigned int align) >> { >> ... >> mutex_lock(&cma_mutex); >> ... >> for (;;) { >> pageno =3D bitmap_find_next_zero_area(cma->bitmap, cma-= >count, >> start, count, mask); >> if (pageno >=3D cma->count) >> break; >> >> pfn =3D cma->base_pfn + pageno; >> + bitmap_set(cma->bitmap, pageno, count); >> + mutex_unlock(&cma_mutex); >> ret =3D alloc_contig_range(pfn, pfn + count, MIGRATE_CM= A); >> + mutex_lock(&cma_mutex); >> if (ret =3D=3D 0) { >> - bitmap_set(cma->bitmap, pageno, count); >> page =3D pfn_to_page(pfn); >> break; >> - } else if (ret !=3D -EBUSY) { >> + } >> + bitmap_clear(cma->bitmap, pageno, count); >> + if (ret !=3D -EBUSY) { >> break; >> } >> ... >> mutex_unlock(&cma_mutex); >> pr_debug("%s(): returned %p\n", __func__, page); >> return page; >> } Like Marek said, this will fail if two concurrent calls to alloc_contig_range are made such that they operate on the same pageblock (which is possible as the allocated regions do not need to be pageblock aligned). Another mutex could be added just for this one call, but as I understand this would not solve the problem. >> bool dma_release_from_contiguous(struct device *dev, struct page *pages, >> int count) >> { >> ... >> + free_contig_range(pfn, count); >> mutex_lock(&cma_mutex); >> bitmap_clear(cma->bitmap, pfn - cma->base_pfn, count); >> - free_contig_range(pfn, count); >> mutex_unlock(&cma_mutex); >> ... >> } This *should* be fine. Didn't test it. --=20 Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=3D./ `o ..o | Computer Science, Micha=C5=82 =E2=80=9Cmina86=E2=80=9D Nazarewicz = (o o) ooo +------ooO--(_)--Ooo-- --=-=-= Content-Type: multipart/signed; boundary="==-=-="; micalg=pgp-sha1; protocol="application/pgp-signature" --==-=-= Content-Type: text/plain --==-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQIcBAEBAgAGBQJTA5voAAoJECBgQBJQdR/0IUoP/0QrRz+dF5SPqjnUVIuo0bl9 97+SmjYHz2E86VgUKB3fXwD+Aj8nNqVLoyjX1BSPgteqhK0ivk187bDtCxEvGdGa z7K5KbNdPp5tMTti/YYbouXmRGD+w/5goyvbwoIe0FGbAoaFBrx0znYR3l2m2DpN 45yS0OdJmzQJMJhv+Nj9dIjxT08HJSlcm/x1gvfdPJxx+CKKZHuT3L93fp9mpUx3 VSz84AtIO+MHz6Oj/08c56c+1QDRVk3T2CMDzWiWA1Sry1oxebQUTTsR+kJC5tmu +PkKMSOZtbx9tQEBVdWQ1g852lLN+yBegZHutaeYAev292XUIxJrZi4v+eghlm1a zIJ9pC97tJ8Vuu7UVa0gmCCKGiXNxGe+FdR8oSFhngAbV0WjcWAIEDqzJ5ON0XwZ l4hQ2NlyF+obOvq4yEJA9Gajt0uo7iUXLkK0aEWJ3AP75ANFHY3N6YrHlwbzW39y pqp+LoIsb90aagtCkGN63OjJJwcE2wl5ldcYwNJN8DoKCFwiXGFHLPomPNNaturF 9/v5T+2+BfN6QiFamn91hL+j2U4yh3+gSf8qZuwY0cRkMO8f/xILk1imwrW9D0yr elDX3JnENq0kCom04pkmQzaJ7s3hQv6oZnWXPLAKCk9BQtfWm4RJL/2uEd/qO+Q9 USynYOm5rOqkGt6jX8j4 =mbCW -----END PGP SIGNATURE----- --==-=-=-- --=-=-=--