Propper use of pci_map_sg

[malte.vesper@postgrad.manchester.ac.uk (Malte Vesper)]

Since my last mail went unanswered I did some further investigation. I 
compiled a kernel with the DMA-API debug fs support and got the dmesg 
output below. Note how I run the program 3 times and it only reports on 
the third run that the page mapping count is off. The thing confusing me 
the most about this, is that I can't see where I go wrong. Since I call 
pci_map_sg and pci_unmap_sg directly after each other there is no room 
for parameter modification. (I have only one device, and the interrupt 
handler has output when invoked). So what is wrong with:

                 mapped =*pci_map_sg*(pcidev, scatterlist, pinned, 
DMA_BIDIRECTIONAL);
*pci_unmap_sg*(pcidev, scatterlist, pinned, DMA_BIDIRECTIONAL);

Do I have to recreate the vanilla scatterlist for pci_unmap_sg?

Any hints/help is highly appreciated.

Ted



Dmesg output:

    [ 2087.171247] SCAS FPGA 0000:01:00.0: [fpga+]: Removing device 0
    [ 2087.171771] [fpga+]: SCAS MAJOR UNREGISTERED: 100
    [ 2087.180070] [fpga+]: fpga+ registered with major number 100
    [ 2087.180096] SCAS FPGA 0000:01:00.0: Probing
    [ 2087.180163] SCAS FPGA 0000:01:00.0: irq 66 for MSI/MSI-X
    [ 2087.180182] SCAS FPGA 0000:01:00.0: [fpga+]: Board tied to slot 0
    [ 2092.359203] [fpga+]: IOCTL 2148040970
    [ 2092.359206] [fpga+]: MINOR: 0
    [ 2092.359207] [fpga+]: ARG: 140736686734672
    [ 2092.359210] SCAS FPGA 0000:01:00.0: [fpga+]: IOCTL:
    IOCTL_FPGA_PIN_PAGE
    [ 2092.359211] Testers hell
    [ 2092.359215] pinned 2
    [ 2092.359216] setting page: 0
    [ 2092.359217] setting page: 1
    [ 2092.359223] Mapped: 2
    [ 2092.359227] Done
    [ 2117.846740] [fpga+]: IOCTL 2148040970
    [ 2117.846742] [fpga+]: MINOR: 0
    [ 2117.846743] [fpga+]: ARG: 140735106116944
    [ 2117.846746] SCAS FPGA 0000:01:00.0: [fpga+]: IOCTL:
    IOCTL_FPGA_PIN_PAGE
    [ 2117.846746] Testers hell
    [ 2117.846749] pinned 2
    [ 2117.846749] setting page: 0
    [ 2117.846750] setting page: 1
    [ 2117.846755] Mapped: 2
    [ 2117.846759] Done
    [ 2124.136132] [fpga+]: IOCTL 2148040970
    [ 2124.136134] [fpga+]: MINOR: 0
    [ 2124.136135] [fpga+]: ARG: 140735560133008
    [ 2124.136138] SCAS FPGA 0000:01:00.0: [fpga+]: IOCTL:
    IOCTL_FPGA_PIN_PAGE
    [ 2124.136138] Testers hell
    [ 2124.136141] pinned 2
    [ 2124.136142] setting page: 0
    [ 2124.136142] setting page: 1
    [ 2124.136147] Mapped: 2
    [ 2124.136152] Done
    [ 2124.136251] BUG: Bad page map in process dma pte:8000000f7b983867
    pmd:fa9d31067
    [ 2124.136254] page:ffffea003dee60c0 count:1 mapcount:-30705
    mapping:ffff880fadddb901 index:0xc0054000afddc901
    [ 2124.136254] flags:
    0x2ffff000008006c(referenced|uptodate|lru|active|swapbacked)
    [ 2124.136257] page dumped because: bad pte
    [ 2124.136258] addr:0000000001382000 vm_flags:08100073
    anon_vma:ffff880fadddb900 mapping:          (null) index:1382
    [ 2124.136261] CPU: 6 PID: 6902 Comm: dma Tainted: G    B   W  OE
    3.18.5hotdog #2
    [ 2124.136261] Hardware name: System manufacturer System Product
    Name/RAMPAGE IV BLACK EDITION, BIOS 0701 06/04/2014
    [ 2124.136262]  ffff880fb842eac8 ffff880fd4093c58 ffffffff8176ab0c
    0000000000000000
    [ 2124.136264]  0000000001382000 ffff880fd4093ca8 ffffffff8119215a
    8000000f7b983867
    [ 2124.136265]  0000000000001382 ffff880fd4093ca8 ffff880fa9d31c10
    ffffea003dee60c0
    [ 2124.136267] Call Trace:
    [ 2124.136270]  [<ffffffff8176ab0c>] dump_stack+0x46/0x58
    [ 2124.136274]  [<ffffffff8119215a>] print_bad_pte+0x1aa/0x250
    [ 2124.136275]  [<ffffffff8119367f>] unmap_single_vma+0x76f/0x8f0
    [ 2124.136278]  [<ffffffff81175cf0>] ? put_pages_list+0x70/0x70
    [ 2124.136279]  [<ffffffff811942d1>] unmap_vmas+0x51/0xa0
    [ 2124.136281]  [<ffffffff8119d48c>] exit_mmap+0x9c/0x170
    [ 2124.136284]  [<ffffffff8106c1c4>] mmput+0x64/0x130
    [ 2124.136286]  [<ffffffff810716ec>] do_exit+0x27c/0xa80
    [ 2124.136287]  [<ffffffff81071f7f>] do_group_exit+0x3f/0xa0
    [ 2124.136290]  [<ffffffff81071ff4>] SyS_exit_group+0x14/0x20
    [ 2124.136292]  [<ffffffff81772f6d>] system_call_fastpath+0x16/0x1b
    [ 2124.136319] BUG: Bad page state in process dma  pfn:f7b983
    [ 2124.136320] page:ffffea003dee60c0 count:0 mapcount:-30705
    mapping:          (null) index:0xc0054000afddc901
    [ 2124.136321] flags: 0x2ffff000008000c(referenced|uptodate|swapbacked)
    [ 2124.136322] page dumped because: nonzero mapcount
    [ 2124.136323] Modules linked in: fpga+(OE) hid_generic nfsv3
    rpcsec_gss_krb5 nfsv4 vmw_vsock_vmci_transport vsock vmw_vmci
    autofs4 nfsd auth_rpcgss nfs_acl nfs snd_hda_codec_realtek
    snd_hda_codec_generic snd_hda_codec_hdmi snd_hda_intel
    snd_hda_controller snd_hda_codec x86_pkg_temp_thermal
    intel_powerclamp snd_hwdep coretemp rfcomm snd_pcm kvm_intel kvm
    bnep lockd bluetooth snd_seq_midi snd_seq_midi_event snd_rawmidi
    snd_seq grace sunrpc eeepc_wmi asus_wmi snd_seq_device snd_timer
    sparse_keymap joydev video mei_me sb_edac snd edac_core mei
    serio_raw lpc_ich soundcore fscache binfmt_misc nls_iso8859_1
    parport_pc ppdev mac_hid tpm_infineon cp210x usbserial lp parport
    dm_crypt hid_microsoft usbhid hid radeon i2c_algo_bit ttm
    drm_kms_helper mxm_wmi drm crct10dif_pclmul crc32_pclmul e1000e
    ghash_clmulni_intel aesni_intel psmouse aes_x86_64 lrw gf128mul
    glue_helper ablk_helper cryptd aacraid ahci ptp libahci pps_core wmi
    [last unloaded: fpga+]
    [ 2124.136351] CPU: 6 PID: 6902 Comm: dma Tainted: G    B   W  OE
    3.18.5hotdog #2
    [ 2124.136352] Hardware name: System manufacturer System Product
    Name/RAMPAGE IV BLACK EDITION, BIOS 0701 06/04/2014
    [ 2124.136353]  ffffffff81aa55c7 ffff880fd4093bb8 ffffffff8176ab0c
    0000000000000000
    [ 2124.136354]  ffffea003dee60c0 ffff880fd4093be8 ffffffff81767527
    ff0000ffffffffff
    [ 2124.136355]  ffffea003dee60c0 0000000000000000 00ffff0000000000
    ffff880fd4093c38
    [ 2124.136356] Call Trace:
    [ 2124.136358]  [<ffffffff8176ab0c>] dump_stack+0x46/0x58
    [ 2124.136360]  [<ffffffff81767527>] bad_page.part.50+0xe0/0xfe
    [ 2124.136362]  [<ffffffff8116c91d>] free_pages_prepare+0x16d/0x190
    [ 2124.136363]  [<ffffffff8116f1a5>] free_hot_cold_page+0x35/0x180
    [ 2124.136365]  [<ffffffff8116f33e>] free_hot_cold_page_list+0x4e/0xa0
    [ 2124.136366]  [<ffffffff81176076>] release_pages+0x1f6/0x270
    [ 2124.136368]  [<ffffffff811a88bd>] free_pages_and_swap_cache+0x8d/0xa0
    [ 2124.136370]  [<ffffffff81191b04>] tlb_flush_mmu_free+0x34/0x60
    [ 2124.136371]  [<ffffffff81192524>] tlb_flush_mmu+0x24/0x30
    [ 2124.136373]  [<ffffffff81192544>] tlb_finish_mmu+0x14/0x40
    [ 2124.136374]  [<ffffffff8119d4bb>] exit_mmap+0xcb/0x170
    [ 2124.136376]  [<ffffffff8106c1c4>] mmput+0x64/0x130
    [ 2124.136378]  [<ffffffff810716ec>] do_exit+0x27c/0xa80
    [ 2124.136379]  [<ffffffff81071f7f>] do_group_exit+0x3f/0xa0
    [ 2124.136381]  [<ffffffff81071ff4>] SyS_exit_group+0x14/0x20
    [ 2124.136382]  [<ffffffff81772f6d>] system_call_fastpath+0x16/0x1b
    ted at ted-headlessBrute:~$





On 29/01/15 19:50, Malte Vesper wrote:
> Hi,
> I am trying to use pci_map_sg in combination with get_user_pages_fast 
> for a driver. However my code screws the processes memory map over. 
> For easier testing I bundled the piinin/unpinning and mapping 
> unmapping into one ioctl call. The following code misses all the 
> checks on return values, since it is only inteneded as a MWE.
>
> When I run my code I get a "*BUG: Bad page map in process ...*", after 
> "Done" is printed.
>
> I tried following DMA-API-howto.txt and looking at other code, but I 
> fail to see where I go wrong.
>
> Regards, Ted
>
>
> Code from the IOCTL handler:
>
>         case IOCTL_FPGA_PIN_PAGE:
>         {
>             struct pageInfo pageInfo;
>
>             dev_dbg(&pcidev->dev, pr_fmt("IOCTL: IOCTL_FPGA_PIN_PAGE\n"));
>
>             if(!copy_from_user(&pageInfo, (void*)arg, sizeof(struct 
> pageInfo))) {
>                 //horrible test
>                 const int noPages = pageInfo.size/PAGE_SIZE;
>                 int pinned;
>                 int mapped  = 0;
>                 struct scatterlist* scatterlist;
>                 printk("Test start\n");
>                 //userspacestartpointer, nopages, write?, page* array
>                 struct page** pages=kmalloc(sizeof(struct 
> page*)*noPages, GFP_KERNEL);
>                 pinned=*get_user_pages_fast*((unsigned 
> long)pageInfo.start, noPages, 1, pages);
>
>                 scatterlist = kmalloc(sizeof(struct 
> scatterlist)*pinned, GFP_KERNEL);
>
>                 for(int i=0; i<pinned; ++i) {
>                     sg_set_page(&scatterlist[i], pages[i], PAGE_SIZE, 0);
>                 }
>
>                 mapped =*pci_map_sg*(pcidev, scatterlist, pinned, 
> DMA_BIDIRECTIONAL);
> *pci_unmap_sg*(pcidev, scatterlist, pinned, DMA_BIDIRECTIONAL);
>
>                 for(int i=0; i<pinned; ++i) {
> *put_page*(pages[i]); //I did place a print here and got two pages 
> unpinned as I expected
>                 }
>                 kfree(scatterlist);
>                 kfree(pages);
>                 printk("Done\n");
>                 /*pageInfo.pageId = getPageId(getArea(&pageInfo));
>                 copy_to_user((void*)arg, &pageInfo, sizeof(struct 
> pageInfo));*/
>                 return pageInfo.pageId;
>             } else {
>                 return -EFAULT;
>             }
>         }
>             break;
>
> P.S.: I used the following code to allocate the memory in userspace, 
> and I use chunk and chunksize to fill pageInfo.start and pageInfo.size 
> respectivly:
>
>     const int pagesize = sysconf(_SC_PAGESIZE);
>     const int chunksize = 2*pagesize;
>     void* chunk;
>
>     if(int error = posix_memalign(&chunk, pagesize, chunksize)) {
>         std::cout << "Could not get a page." << std::endl;
>         return error;
>     }
>
>
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