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Thu, 17 Dec 2020 12:12:23 -0800 Received: by devvm3388.prn0.facebook.com (Postfix, from userid 111017) id 30DEB20F4781; Thu, 17 Dec 2020 12:12:15 -0800 (PST) From: Roman Gushchin To: Andrew Morton , Mike Rapoport , CC: Joonsoo Kim , Rik van Riel , Michal Hocko , , , Roman Gushchin Subject: [PATCH v2 2/2] memblock: do not start bottom-up allocations with kernel_end Date: Thu, 17 Dec 2020 12:12:14 -0800 Message-ID: <20201217201214.3414100-2-guro@fb.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20201217201214.3414100-1-guro@fb.com> References: <20201217201214.3414100-1-guro@fb.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2020-12-17_14:2020-12-17,2020-12-17 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 priorityscore=1501 bulkscore=0 mlxlogscore=999 lowpriorityscore=0 clxscore=1015 spamscore=0 suspectscore=0 phishscore=0 impostorscore=0 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012170134 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org With kaslr the kernel image is placed at a random place, so starting the bottom-up allocation with the kernel_end can result in an allocation failure and a warning like this one: [ 0.002920] hugetlb_cma: reserve 2048 MiB, up to 2048 MiB per node [ 0.002921] ------------[ cut here ]------------ [ 0.002922] memblock: bottom-up allocation failed, memory hotremove ma= y be affected [ 0.002937] WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_= in_range_node+0x178/0x25a [ 0.002937] Modules linked in: [ 0.002939] CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0+ #1169 [ 0.002940] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIO= S 1.14.0-1.fc33 04/01/2014 [ 0.002942] RIP: 0010:memblock_find_in_range_node+0x178/0x25a [ 0.002944] Code: e9 6d ff ff ff 48 85 c0 0f 85 da 00 00 00 80 3d 9b 3= 5 df 00 00 75 15 48 c7 c7 c0 75 59 88 c6 05 8b 35 df 00 01 e8 25 8a fa ff= <0f> 0b 48 c7 44 24 20 ff ff ff ff 44 89 e6 44 89 ea 48 c7 c1 70 5c [ 0.002945] RSP: 0000:ffffffff88803d18 EFLAGS: 00010086 ORIG_RAX: 0000= 000000000000 [ 0.002947] RAX: 0000000000000000 RBX: 0000000240000000 RCX: 00000000f= fffdfff [ 0.002948] RDX: 00000000ffffdfff RSI: 00000000ffffffea RDI: 000000000= 0000046 [ 0.002948] RBP: 0000000100000000 R08: ffffffff88922788 R09: 000000000= 0009ffb [ 0.002949] R10: 00000000ffffe000 R11: 3fffffffffffffff R12: 000000000= 0000000 [ 0.002950] R13: 0000000000000000 R14: 0000000080000000 R15: 00000001f= b42c000 [ 0.002952] FS: 0000000000000000(0000) GS:ffffffff88f71000(0000) knlG= S:0000000000000000 [ 0.002953] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 0.002954] CR2: ffffa080fb401000 CR3: 00000001fa80a000 CR4: 000000000= 00406b0 [ 0.002956] Call Trace: [ 0.002961] ? memblock_alloc_range_nid+0x8d/0x11e [ 0.002963] ? cma_declare_contiguous_nid+0x2c4/0x38c [ 0.002964] ? hugetlb_cma_reserve+0xdc/0x128 [ 0.002968] ? flush_tlb_one_kernel+0xc/0x20 [ 0.002969] ? native_set_fixmap+0x82/0xd0 [ 0.002971] ? flat_get_apic_id+0x5/0x10 [ 0.002973] ? register_lapic_address+0x8e/0x97 [ 0.002975] ? setup_arch+0x8a5/0xc3f [ 0.002978] ? start_kernel+0x66/0x547 [ 0.002980] ? load_ucode_bsp+0x4c/0xcd [ 0.002982] ? secondary_startup_64_no_verify+0xb0/0xbb [ 0.002986] random: get_random_bytes called from __warn+0xab/0x110 wit= h crng_init=3D0 [ 0.002988] ---[ end trace f151227d0b39be70 ]--- At the same time, the kernel image is protected with memblock_reserve(), so we can just start searching at PAGE_SIZE. In this case the bottom-up allocation has the same chances to success as a top-down allocation, so there is no reason to fallback in the case of a failure. All together it simplifies the logic. Signed-off-by: Roman Gushchin --- mm/memblock.c | 49 ++++++------------------------------------------- 1 file changed, 6 insertions(+), 43 deletions(-) diff --git a/mm/memblock.c b/mm/memblock.c index b68ee86788af..10bd7d1ef0f4 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -275,14 +275,6 @@ __memblock_find_range_top_down(phys_addr_t start, ph= ys_addr_t end, * * Find @size free area aligned to @align in the specified range and nod= e. * - * When allocation direction is bottom-up, the @start should be greater - * than the end of the kernel image. Otherwise, it will be trimmed. The - * reason is that we want the bottom-up allocation just near the kernel - * image so it is highly likely that the allocated memory and the kernel - * will reside in the same node. - * - * If bottom-up allocation failed, will try to allocate memory top-down. - * * Return: * Found address on success, 0 on failure. */ @@ -291,8 +283,6 @@ static phys_addr_t __init_memblock memblock_find_in_r= ange_node(phys_addr_t size, phys_addr_t end, int nid, enum memblock_flags flags) { - phys_addr_t kernel_end, ret; - /* pump up @end */ if (end =3D=3D MEMBLOCK_ALLOC_ACCESSIBLE || end =3D=3D MEMBLOCK_ALLOC_KASAN) @@ -301,40 +291,13 @@ static phys_addr_t __init_memblock memblock_find_in= _range_node(phys_addr_t size, /* avoid allocating the first page */ start =3D max_t(phys_addr_t, start, PAGE_SIZE); end =3D max(start, end); - kernel_end =3D __pa_symbol(_end); - - /* - * try bottom-up allocation only when bottom-up mode - * is set and @end is above the kernel image. - */ - if (memblock_bottom_up() && end > kernel_end) { - phys_addr_t bottom_up_start; - - /* make sure we will allocate above the kernel */ - bottom_up_start =3D max(start, kernel_end); =20 - /* ok, try bottom-up allocation first */ - ret =3D __memblock_find_range_bottom_up(bottom_up_start, end, - size, align, nid, flags); - if (ret) - return ret; - - /* - * we always limit bottom-up allocation above the kernel, - * but top-down allocation doesn't have the limit, so - * retrying top-down allocation may succeed when bottom-up - * allocation failed. - * - * bottom-up allocation is expected to be fail very rarely, - * so we use WARN_ONCE() here to see the stack trace if - * fail happens. - */ - WARN_ONCE(IS_ENABLED(CONFIG_MEMORY_HOTREMOVE), - "memblock: bottom-up allocation failed, memory hotremove may be aff= ected\n"); - } - - return __memblock_find_range_top_down(start, end, size, align, nid, - flags); + if (memblock_bottom_up()) + return __memblock_find_range_bottom_up(start, end, size, align, + nid, flags); + else + return __memblock_find_range_top_down(start, end, size, align, + nid, flags); } =20 /** --=20 2.26.2