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[79.139.233.37]) by smtp.googlemail.com with ESMTPSA id 21sm1055977ljv.19.2020.01.29.06.21.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Jan 2020 06:21:58 -0800 (PST) Subject: Re: [PATCH 3/5] mm/mremap: use pmd_addr_end to calculate next in move_page_tables() To: Russell King - ARM Linux admin Cc: Wei Yang , akpm@linux-foundation.org, dan.j.williams@intel.com, aneesh.kumar@linux.ibm.com, kirill@shutemov.name, yang.shi@linux.alibaba.com, thellstrom@vmware.com, Thierry Reding , Jon Hunter , linux-kernel@vger.kernel.org, linux-mm@kvack.org, "linux-tegra@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" References: <20200117232254.2792-1-richardw.yang@linux.intel.com> <20200117232254.2792-4-richardw.yang@linux.intel.com> <7147774a-14e9-4ff3-1548-4565f0d214d5@gmail.com> <20200129094738.GE25745@shell.armlinux.org.uk> From: Dmitry Osipenko Message-ID: <2791a187-ec3e-6b78-515f-25e7559a3749@gmail.com> Date: Wed, 29 Jan 2020 17:21:55 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20200129094738.GE25745@shell.armlinux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 29.01.2020 12:47, Russell King - ARM Linux admin =D0=BF=D0=B8=D1=88=D0=B5= =D1=82: > On Sun, Jan 26, 2020 at 05:47:57PM +0300, Dmitry Osipenko wrote: >> 18.01.2020 02:22, Wei Yang =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>> Use the general helper instead of do it by hand. >>> >>> Signed-off-by: Wei Yang >>> --- >>> mm/mremap.c | 7 ++----- >>> 1 file changed, 2 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/mremap.c b/mm/mremap.c >>> index c2af8ba4ba43..a258914f3ee1 100644 >>> --- a/mm/mremap.c >>> +++ b/mm/mremap.c >>> @@ -253,11 +253,8 @@ unsigned long move_page_tables(struct vm_area_st= ruct *vma, >>> =20 >>> for (; old_addr < old_end; old_addr +=3D extent, new_addr +=3D exte= nt) { >>> cond_resched(); >>> - next =3D (old_addr + PMD_SIZE) & PMD_MASK; >>> - /* even if next overflowed, extent below will be ok */ >>> + next =3D pmd_addr_end(old_addr, old_end); >>> extent =3D next - old_addr; >>> - if (extent > old_end - old_addr) >>> - extent =3D old_end - old_addr; >>> old_pmd =3D get_old_pmd(vma->vm_mm, old_addr); >>> if (!old_pmd) >>> continue; >>> @@ -301,7 +298,7 @@ unsigned long move_page_tables(struct vm_area_str= uct *vma, >>> =20 >>> if (pte_alloc(new_vma->vm_mm, new_pmd)) >>> break; >>> - next =3D (new_addr + PMD_SIZE) & PMD_MASK; >>> + next =3D pmd_addr_end(new_addr, new_addr + len); >>> if (extent > next - new_addr) >>> extent =3D next - new_addr; >>> move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma, >>> >> >> Hello Wei, >> >> Starting with next-20200122, I'm seeing the following in KMSG on NVIDI= A >> Tegra (ARM32): >> >> BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:190 >> >> and eventually kernel hangs. >> >> Git's bisection points to this patch and reverting it helps. Please fi= x, >> thanks in advance. >=20 > The above is definitely wrong - pXX_addr_end() are designed to be used > with an address index within the pXX table table and the address index > of either the last entry in the same pXX table or the beginning of the > _next_ pXX table. Arbitary end address indicies are not allowed. >=20 > When page tables are "rolled up" when levels don't exist, it is common > practice for these macros to just return their end address index. > Hence, if they are used with arbitary end address indicies, then the > iteration will fail. >=20 > The only way to do this is: >=20 > next =3D pmd_addr_end(old_addr, > pud_addr_end(old_addr, > p4d_addr_end(old_addr, > pgd_addr_end(old_addr, old_end)))); >=20 > which gives pmd_addr_end() (and each of the intermediate pXX_addr_end()= ) > the correct end argument. However, that's a more complex and verbose, > and likely less efficient than the current code. >=20 > I'd suggest that there's nothing to "fix" in the v5.5 code wrt this, > and trying to "clean it up" will just result in less efficient or > broken code. >=20 Hello Russell, Thank you very much for the extra clarification!