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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <51586a9d-6461-bae2-c3e4-fce5f19bd786@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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: On 18.12.19 09:53, David Hildenbrand wrote: > On 18.12.19 04:21, Dan Williams wrote: >> On Tue, Dec 17, 2019 at 2:47 AM David Hildenbrand wrote: >>> >>> When we remove an early section, we don't free the usage map, as the >>> usage maps of other sections are placed into the same page. Once the >>> section is removed, it is no longer an early section (especially, the >>> memmap is freed). When we re-add that section, the usage map is reused, >>> however, it is no longer an early section. When removing that section >>> again, we try to kfree() a usage map that was allocated during early >>> boot - bad. >>> >>> Let's check against PageReserved() to see if we are dealing with an usage >>> map that was allocated during boot. We could also check against >>> !(PageSlab(usage_page) || PageCompound(usage_page)), but PageReserved() >>> is cleaner. >>> >>> Can be triggered using memtrace under ppc64/powernv: >>> >>> $ mount -t debugfs none /sys/kernel/debug/ >>> $ echo 0x20000000 > /sys/kernel/debug/powerpc/memtrace/enable >>> $ echo 0x20000000 > /sys/kernel/debug/powerpc/memtrace/enable >>> [ 12.093442] ------------[ cut here ]------------ >>> [ 12.093469] kernel BUG at mm/slub.c:3969! >>> [ 12.093656] Oops: Exception in kernel mode, sig: 5 [#1] >>> [ 12.093961] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA PowerNV >>> [ 12.094320] Modules linked in: >>> [ 12.094615] CPU: 0 PID: 154 Comm: sh Not tainted 5.5.0-rc2-next-20191216-00005-g0be1dba7b7c0 #61 >>> [ 12.095066] NIP: c000000000396b38 LR: c000000000385848 CTR: c000000000143d30 >>> [ 12.095427] REGS: c000000073077680 TRAP: 0700 Not tainted (5.5.0-rc2-next-20191216-00005-g0be1dba7b7c0) >>> [ 12.095886] MSR: 900000000282b033 CR: 28004828 XER: 20000000 >>> [ 12.096395] CFAR: c000000000396b9c IRQMASK: 0 >>> [ 12.096395] GPR00: c000000000385848 c000000073077910 c00000000110f300 c00000007ffffc00 >>> [ 12.096395] GPR04: 0000000000000000 ffffffffffffffff 0000000000000000 0000000000000000 >>> [ 12.096395] GPR08: 0000000000000000 0000000000000001 0000000000000000 ffffffffffffffc8 >>> [ 12.096395] GPR12: 0000000000004000 c0000000012d0000 0000000000001000 c000000000d33c78 >>> [ 12.096395] GPR16: 0000000000000000 c0000000011bfeb0 ffffffffffffe000 c0000000000b6370 >>> [ 12.096395] GPR20: ffffffffe0000000 c0000000011411c0 0000000000006000 c0000000000b6390 >>> [ 12.096395] GPR24: 0000000010000000 0000000000000040 0000000000000000 0000000000000000 >>> [ 12.096395] GPR28: c000000000385848 c00c0000001fffc0 0000000000004000 0000000000000000 >>> [ 12.099882] NIP [c000000000396b38] kfree+0x338/0x3b0 >>> [ 12.100135] LR [c000000000385848] section_deactivate+0x138/0x200 >>> [ 12.100508] Call Trace: >>> [ 12.100927] [c000000073077910] [c0000000010599a8] 0xc0000000010599a8 (unreliable) >>> [ 12.101338] [c000000073077960] [c000000000385848] section_deactivate+0x138/0x200 >>> [ 12.101696] [c000000073077a10] [c00000000039b9f4] __remove_pages+0x114/0x150 >>> [ 12.102025] [c000000073077a60] [c00000000006793c] arch_remove_memory+0x3c/0x160 >>> [ 12.102381] [c000000073077ae0] [c00000000039c154] try_remove_memory+0x114/0x1a0 >>> [ 12.102715] [c000000073077b90] [c00000000039c020] __remove_memory+0x20/0x40 >>> [ 12.103041] [c000000073077bb0] [c0000000000b6714] memtrace_enable_set+0x254/0x850 >>> [ 12.103402] [c000000073077cb0] [c0000000004197e8] simple_attr_write+0x138/0x160 >>> [ 12.103751] [c000000073077d10] [c000000000558c9c] full_proxy_write+0x8c/0x110 >>> [ 12.104100] [c000000073077d60] [c0000000003d02a8] __vfs_write+0x38/0x70 >>> [ 12.104409] [c000000073077d80] [c0000000003d3c5c] vfs_write+0x11c/0x2a0 >>> [ 12.104711] [c000000073077dd0] [c0000000003d4054] ksys_write+0x84/0x140 >>> [ 12.105011] [c000000073077e20] [c00000000000b594] system_call+0x5c/0x68 >>> [ 12.105357] Instruction dump: >>> [ 12.105606] e93d0000 75290001 41820090 8bfd0051 38a0ffff 7ca5f830 7bff0020 7ca507b4 >>> [ 12.105993] e95d0000 39200000 754a0001 4182005c <0b090000> 893d0007 3d42000b 38800006 >>> [ 12.106583] ---[ end trace 4b053cbd84e0db62 ]--- >>> >>> The first invocation will offline+remove memory blocks. The second >>> invocation will first add+online them again, in order to offline+remove >>> them again (usually we are lucky and the exact same memory blocks will >>> get "reallocated"). >>> >>> Tested on powernv with boot memory: The usage map will not get freed. >>> Tested on x86-64 with DIMMs: The usage map will get freed. >>> >>> Fixes: 326e1b8f83a4 ("mm/sparsemem: introduce a SECTION_IS_EARLY flag") >>> Cc: Andrew Morton >>> Cc: Dan Williams >>> Cc: Oscar Salvador >>> Cc: Michal Hocko >>> Signed-off-by: David Hildenbrand >>> --- >>> mm/sparse.c | 9 ++++++++- >>> 1 file changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/sparse.c b/mm/sparse.c >>> index b20ab7cdac86..3822ecbd8a1f 100644 >>> --- a/mm/sparse.c >>> +++ b/mm/sparse.c >>> @@ -777,7 +777,14 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, >>> if (bitmap_empty(subsection_map, SUBSECTIONS_PER_SECTION)) { >>> unsigned long section_nr = pfn_to_section_nr(pfn); >>> >>> - if (!section_is_early) { >> >> With this change this function no longer needs a local >> section_is_early variable... > > Right. I'll send a cleanup patch and we can decide if we want to squash > them in Andrews tree. Ah, just realized that we cannot do that. ms->section_mem_map = sparse_encode_mem_map(NULL, section_nr) already clears the early flag, so inlining that condition would break it. -- Thanks, David / dhildenb