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Date:	Tue, 15 Jul 2014 00:13:26 +0400
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Ingo Korb <ingo.korb@...dortmund.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ning Qu <quning@...gle.com>, Dave Jones <davej@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: PROBLEM: repeated remap_file_pages on tmpfs triggers bug on
 process exit

It seems boundng logic in do_fault_around is wrong:

start_addr = max(address & fault_around_mask(), vma->vm_start);
off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
pte -= off;
pgoff -= off;

Ok, off  <= 511, but it might be bigger than pte offset in pte table.
So after pte -= off pte points into previous page.

/*
*  max_pgoff is either end of page table or end of vma
*  or fault_around_pages() from pgoff, depending what is nearest.
*/
max_pgoff = pgoff - ((start_addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +
PTRS_PER_PTE - 1;
max_pgoff = min3(max_pgoff, vma_pages(vma) + vma->vm_pgoff - 1,
pgoff + fault_around_pages() - 1);



On Mon, Jul 14, 2014 at 11:22 PM, Hugh Dickins <hughd@...gle.com> wrote:
> On Mon, 14 Jul 2014, Ingo Korb wrote:
>
>> Hi,
>>
>> repeated mapping of the same file on tmpfs using remap_file_pages
>> sometimes triggers a "BUG at mm/filemap.c:202" when the process exits, log
>> message below. The system is an x86_64 VirtualBox machine with 2GB of RAM
>> running Debian, but it could also be reproduced on a non-virtualized
>> laptop.
>>
>> The bug can be triggered in Linux 3.16-rc5, bisecting has located d7c17551
>> as the first failing commit (mm: implement ->map_pages for shmem/tmpfs).
>>
>> A test program for this has been attached (I don't trust this webmailer to
>> not mangle it). With the parameters set in the source code, the BUG
>> message should be triggered within a small number of tries (usually the
>> first or second). Changing the size of the memory map sometimes delays the
>> bug ("while true; do ./remap-demo; done" should still trigger it within a
>> few seconds) or avoids it completely - I don't see any patterns yet. Using
>> (at least) two different mappings for the file, each of which has been
>> remapped seem to be a requirement for triggering it.
>>
>> Implementing the same mappings using mmap() does not appear to cause any
>> problems, but I assume that someone might care about this problem while
>> remap_file_pages() is still in the kernel.
>
> This is very good news :)  Thank you so much for going to all this
> trouble over it.  If you didn't realize, yours is not the first report
> of an mm/filemap.c:202! BUG_ON(page_mapped(page)), but most of them
> have happened when using the Trinity fuzzer (known to be fond of tmpfs
> and remap_file_pages), and too rare to track down further.
>
> I have several times in recent months eyed the (old) remap_file_pages
> code, and the filemap_map_pages code, hoping to find the answer in one
> or the other; but had no success.
>
> Kirill, Konstantin, would either of you have a moment to try and track
> this down further?  I'd love to, but I am _still_ not finished with the
> fallocate hang business, then sealing review, then plenty beyond that.
> Ingo's remap-demo.c inline below.
>
> Of course, one option will be just to revert d7c17551; but I'd much
> rather track down the bug and fix it, if we can in the next couple of
> weeks - even if it does turn out to be in code removed in 3.17.
>
> Thanks!
> Hugh
>
>>
>> -ik
>>
>>
>> ------------[ cut here ]------------
>> kernel BUG at mm/filemap.c:202!
>> invalid opcode: 0000 [#1] SMP
>> Modules linked in: uinput nfsd auth_rpcgss oid_registry nfs_acl nfs lockd
>> fscache sunrpc ext3 jbd loop joydev hid_generic usbhid hid psmouse
>> parport_pc ohci_pci ohci_hcd ehci_hcd usbcore ac i2c_piix4 pcspkr
>> serio_raw evdev parport battery button processor i2c_core usb_common
>> microcode thermal_sys ext4 crc16 jbd2 mbcache sr_mod cdrom sg sd_mod
>> crc_t10dif crct10dif_common ata_generic e1000 ahci libahci ata_piix libata
>> scsi_mod
>> CPU: 3 PID: 2992 Comm: test Not tainted 3.16.0-rc5ik1 #37
>> Hardware name: innotek GmbH VirtualBox, BIOS VirtualBox 12/01/2006 task:
>> ffff88005a9363d0 ti: ffff880037968000 task.ti: ffff880037968000 RIP:
>> 0010:[<ffffffff810db4d3>]  [<ffffffff810db4d3>]
>> __delete_from_page_cache+0x16f/0x1f6
>> RSP: 0018:ffff88003796bba8  EFLAGS: 00010046
>> RAX: 0000000000000000 RBX: ffffea00012ee220 RCX: 00000000ffffffe2
>> RDX: 0000000000000018 RSI: 0000000000000018 RDI: ffff88005dbeb700
>> RBP: ffff8800378d1c10 R08: ffff88005dbeb700 R09: 0000000000000013
>> R10: 0000000000000013 R11: 0000000000000000 R12: 0000000000000000
>> R13: 0000000000000003 R14: ffff8800378d1c18 R15: 000000000000000f
>> FS:  0000000000000000(0000) GS:ffff88005d980000(0000)
>> knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007f69ad38fa30 CR3: 0000000001611000 CR4: 00000000000006e0
>> Stack:
>>  0000000000000002 000000000000000f ffff880059899008 ffff8800598990a8
>> ffff8800378d1c10 ffffea00012ee220 ffff8800378d1c28 0000000000000000
>> ffff8800378d1ac0 ffff8800374d0600 0000000000000001 ffffffff810db65b
>> Call Trace:
>>  [<ffffffff810db65b>] ? delete_from_page_cache+0x32/0x56
>>  [<ffffffff810e621d>] ? truncate_inode_page+0x62/0x69
>>  [<ffffffff810edf29>] ? shmem_undo_range+0x13f/0x3f3
>>  [<ffffffff810df855>] ? get_pfnblock_flags_mask+0x1d/0x4d
>>  [<ffffffff810e0bcb>] ? free_hot_cold_page+0x76/0x134
>>  [<ffffffff810e528a>] ? release_pages+0x171/0x180
>>  [<ffffffff810e4aa2>] ? hpage_nr_pages+0x1b/0x1b
>>  [<ffffffff811418df>] ? __inode_wait_for_writeback+0x67/0xae
>>  [<ffffffff810ee1e8>] ? shmem_truncate_range+0xb/0x25
>>  [<ffffffff810ee76d>] ? shmem_evict_inode+0x4f/0xed
>>  [<ffffffff810ee71e>] ? shmem_file_setup+0x7/0x7
>>  [<ffffffff81136947>] ? evict+0xa3/0x147
>>  [<ffffffff81133576>] ? __dentry_kill+0x103/0x173
>>  [<ffffffff81133983>] ? dput+0x133/0x150
>>  [<ffffffff8112489d>] ? __fput+0x163/0x184
>>  [<ffffffff8105f10c>] ? task_work_run+0x7b/0x8f
>>  [<ffffffff81049c69>] ? do_exit+0x3f6/0x904
>>  [<ffffffff8104a282>] ? do_group_exit+0x68/0x9a
>>  [<ffffffff8104a2c4>] ? SyS_exit_group+0x10/0x10
>>  [<ffffffff8138fb69>] ? system_call_fastpath+0x16/0x1b
>> Code: be 0a 00 00 00 48 89 df e8 96 5b 01 00 48 8b 03 a9 00 00 08 00 74 0d
>> be 18 00 00 00 48 89 df e8 7f 5b 01 00 8b 43 18 85 c0 78 02 <0f> 0b 48 8b
>> 03 a8 10 74 6f 48 8b 85 88 00 00 00 f6 40 20 01 75
>> RIP  [<ffffffff810db4d3>] __delete_from_page_cache+0x16f/0x1f6
>>  RSP <ffff88003796bba8>
>> ---[ end trace 79ae5bd27fcedca9 ]---
>> Fixing recursive fault but reboot is needed!
>> BUG: Bad rss-counter state mm:ffff88005aae60c0 idx:0 val:1
>
> And that "Bad rss-counter" report fits some of the reports too, good.
>
> Here's Ingo's remap-demo.c inline, but I've not tried it:
>
> #define _GNU_SOURCE
> #include <sys/mman.h>
> #include <sys/resource.h>
> #include <errno.h>
> #include <limits.h>
> #include <malloc.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
>
> #define PAGE_SIZE 4096
> // NOTE: DATA=MAP2=16 seems to trigger in the first few tries
> // NOTE: 9/9 needs a loop and a few seconds to trigger
> // NOTE: DATA=9, MAP2=8 does not trigger
> #define DATA_SIZE 16
> #define MAP2_SIZE 16
>
> int shmfd;
> char shmpath[] = "/dev/shm/mmaptest-XXXXXX";
> unsigned char *map1, *map2;
> unsigned int i;
>
> int main(int argc, char *argv[]) {
>   /* create a data file on tmpfs */
>   shmfd = mkstemp(shmpath);
>   if (shmfd < 0) {
>     perror("mkstemp");
>     exit(2);
>   }
>
>   if (unlink(shmpath)) {
>     perror("unlink");
>     exit(2);
>   }
>
>   if (ftruncate(shmfd, DATA_SIZE * PAGE_SIZE)) {
>     perror("ftruncate");
>     exit(2);
>   }
>
>   /* map a single page from the file */
>   map1 = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
>   if (map1 == MAP_FAILED) {
>     perror("mmap 1");
>     exit(2);
>   }
>
>   /* remap it to another page in the file */
>   // NOTE: Does not trigger without remapping
>   // NOTE: Does not trigger for 7, but does trigger for 8 if both sizes are 16
>   //  (DATA_SIZE-2 is sufficiently generic here)
>   if (remap_file_pages(map1, PAGE_SIZE, 0, DATA_SIZE - 2, MAP_SHARED)) {
>     perror("remap_file_pages 1");
>     exit(2);
>   }
>
>   /* create a second mapping */
>   map2 = mmap(NULL, MAP2_SIZE * PAGE_SIZE, PROT_READ | PROT_WRITE,
>               MAP_SHARED, shmfd, 0);
>   if (map2 == MAP_FAILED) {
>     perror("mmap 2");
>     exit(2);
>   }
>
>   /* map all of its pages to page 0 */
>   // NOTE: Remapping only the last page does not trigger
>   for (i = 0; i < MAP2_SIZE; i++) {
>     if (remap_file_pages(map2 + PAGE_SIZE * i, PAGE_SIZE, 0, 0, MAP_SHARED)) {
>       perror("remap_file_pages 3");
>       exit(2);
>     }
>   }
>
>   close(shmfd);
>
>   exit(0);
> }
--
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