Check for two things: 1. Handle error from mmap() call in user space, it seems munmap is called unconditionally.
while(1) { str = mmap(vma); //always map the same address and offset (they are set to zero), logger will handle this fwrite(str, 4096, fd); munmap(str); } 2. Debug more why logger_vma_fault is failing? Is there a window where you might have buffer list empty while you arrange for new page? -Rajat On Wed, Feb 26, 2014 at 5:31 PM, Le Tan <tamlokv...@gmail.com> wrote: > OK, I will look into this. Is it OK to block vm_fault? > I have another question. In my userspace program, I mmap() my device, > then read something, then munmap() my device() and then mmap() my device > again. The program do this in a loop. Everytime it mmap() the same address > and offset. > My device maintains a list of pages. In vm_operations fault, I just map > the address to the head of the list. And in vm_operations close, I just > delete the head from the list and free the page. > Everything seems to be OK except that after I call the munmap() in the > program, there is an error message. The error seems to happens between the > call of vm_operations fault and vm_operations close. I have posted this > question before ( See > this<http://www.spinics.net/lists/newbies/msg51339.html>). > > [42522.596689] logger_mmap():start:7f8ff57be000, end:7f8ff57bf000 > //this is the mmap() function of my device module > [42522.596694] > logger_vma_fault():vmf->pgoff:0d,start:7f8ff57be000,pgoff:0,offset:0 > //this is the fault function of struct vm_operations_struct > [42522.596729] BUG: Bad page map in process logger_pro > pte:8000000612a30025 pmd:314175067 //this is the error > [42522.596740] page:ffffea00184a8c00 count:2 mapcount:-2146959356 > mapping: (null) index:0xffff880612a36000 > [42522.596747] page flags: 0x200000000004080(slab|head) > [42522.596811] addr:00007f8ff57be000 vm_flags:04040071 anon_vma: > (null) mapping:ffff880613b25f08 index:0 > [42522.596824] vma->vm_ops->fault: logger_vma_fault+0x0/0x140 [logger] > [42522.596834] vma->vm_file->f_op->mmap: logger_mmap+0x0/0xd50 [logger] > [42522.596842] CPU: 1 PID: 21571 Comm: logger_pro Tainted: G B > IO 3.11.0+ #1 > [42522.596844] Hardware name: Dell Inc. PowerEdge M610/000HYJ, BIOS > 2.0.13 04/06/2010 > [42522.596846] 00007f8ff57be000 ffff880314199c98 ffffffff816ad166 > 0000000000006959 > [42522.596851] ffff880314539a98 ffff880314199ce8 ffffffff8114e270 > ffffea00184a8c00 > [42522.596854] 0000000000000000 ffff880314199cc8 00007f8ff57be000 > ffff880314199e18 > [42522.596858] Call Trace: > [42522.596867] [<ffffffff816ad166>] dump_stack+0x46/0x58 > [42522.596872] [<ffffffff8114e270>] print_bad_pte+0x190/0x250 > [42522.596877] [<ffffffff8115027b>] unmap_single_vma+0x6cb/0x7a0 > [42522.596880] [<ffffffff81150bd4>] unmap_vmas+0x54/0xa0 > [42522.596885] [<ffffffff81155aa7>] unmap_region+0xa7/0x110 > [42522.596888] [<ffffffff81157f97>] do_munmap+0x1f7/0x3e0 > [42522.596891] [<ffffffff811581ce>] vm_munmap+0x4e/0x70 > [42522.596904] [<ffffffff811591bb>] SyS_munmap+0x2b/0x40 > [42522.596915] [<ffffffff816bc9c2>] system_call_fastpath+0x16/0x1b > [42522.596920] logger_vma_close():start:7f8ff57be000, > end:7f8ff57bf000, vmas:0 //this is the close function of struct > vm_operations_struct > > So do you have any idea about this error? > Thanks very much! > > > 2014-02-27 9:04 GMT+08:00 Rajat Sharma <fs.ra...@gmail.com>: > > Why do you need to block in mmap()? mmap is supposed to create a mapping >> area in virtual address space for the process. Actual transfer happens >> later through page fault handlers on demand basis. look at vm_operations >> fault/readpage etc methods, these might be the places you want to wait for >> the data. >> >> >> On Wed, Feb 26, 2014 at 4:14 PM, Le Tan <tamlokv...@gmail.com> wrote: >> >>> So what should I do if I want the mmap() not to return right now? Is >>> it strange to block in mmap() and few people will do this? Thanks for >>> your help! >>> >>> 2014-02-27 4:45 GMT+08:00 Rajat Sharma <fs.ra...@gmail.com>: >>> > It seems this task "landscape-sysin" is trying to peek into virtual >>> memory >>> > of your processes and the process within mmap call is holding its >>> > mm->mmap_sem semaphore which grants access to its address space. >>> > landscape-sysin is trying to grab this semaphore to poke into address >>> space >>> > of your mmap process address space. As from your description, it might >>> be >>> > invoked everytime you are opening a new shell. Not sure why this >>> process >>> > bother's about other process address space. Little googling shows this >>> as >>> > relevant to your case: >>> > >>> > >>> http://www.techques.com/question/2-66765/Disable-usage-of-console-kit-daemon-in-Ubuntu >>> > >>> > Your read process is innocent and not involved in this deadlock. >>> > >>> > -Rajat >>> > >>> > >>> > On Wed, Feb 26, 2014 at 4:13 AM, Le Tan <tamlokv...@gmail.com> wrote: >>> >> >>> >> Hi, I am writing a driver module. Now I have some questions about >>> blocked >>> >> I/O. >>> >> my_read() is the read function in the file_operations struct in my >>> >> module. my_read() is just as simple as this: >>> >> ssize_t my_read(....) >>> >> { >>> >> if(wait_event_interruptible(dev->queue, a == b)) >>> >> return -ERESTARTSYS; >>> >> return count; >>> >> } >>> >> Then I write a simple program to open and read the device. Obviously >>> >> the program will be blocked. Now I still can open a new shell window >>> >> and log in ( I use xshell). >>> >> >>> >> However, then I implement my_mmap(), the mmap function in the >>> >> file_operations struct in my module, like this: >>> >> int my_mmap(....) >>> >> { >>> >> if(wait_event_interruptible(dev->queue, a == b)) >>> >> return -ERESTARTSYS; >>> >> return 0; >>> >> } >>> >> Then I write a simple program to open and mmap() the device. Obviously >>> >> the program will be blocked again. However, when I open a new shell >>> >> window in xshell and try to connect to the linux, it displays like >>> >> this: >>> >> >>> >> Connecting to 192.168.146.118:22... >>> >> Connection established. >>> >> To escape to local shell, press 'Ctrl+Alt+]'. >>> >> >>> >> And I can't log in! Then after a while, in the syslog, there is one >>> >> message like this: >>> >> [38306.614103] INFO: task landscape-sysin:17616 blocked for more than >>> >> 120 seconds. >>> >> [38306.614114] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" >>> >> disables this message. >>> >> [38306.614120] landscape-sysin D ffffffff8180fb60 0 17616 17609 >>> >> 0x00000000 >>> >> [38306.614125] ffff88031d609c90 0000000000000082 ffff88032fffdb08 >>> >> 0000000000000000 >>> >> [38306.614130] ffff8803130bdc40 ffff88031d609fd8 ffff88031d609fd8 >>> >> ffff88031d609fd8 >>> >> [38306.614133] ffff88062150c530 ffff8803130bdc40 0000004100000000 >>> >> ffff8803130bdc40 >>> >> [38306.614137] Call Trace: >>> >> [38306.614147] [<ffffffff816b2c49>] schedule+0x29/0x70 >>> >> [38306.614151] [<ffffffff816b3acd>] rwsem_down_read_failed+0x9d/0xf0 >>> >> [38306.614157] [<ffffffff81341824>] >>> call_rwsem_down_read_failed+0x14/0x30 >>> >> [38306.614160] [<ffffffff816b1644>] ? down_read+0x24/0x2b >>> >> [38306.614166] [<ffffffff81153661>] __access_remote_vm+0x41/0x1f0 >>> >> [38306.614170] [<ffffffff81153ddb>] access_process_vm+0x5b/0x80 >>> >> [38306.614175] [<ffffffff811ea423>] proc_pid_cmdline+0x93/0x120 >>> >> [38306.614178] [<ffffffff811eb425>] proc_info_read+0xa5/0xf0 >>> >> [38306.614182] [<ffffffff81186e84>] vfs_read+0xb4/0x180 >>> >> [38306.614185] [<ffffffff81187102>] SyS_read+0x52/0xa0 >>> >> [38306.614189] [<ffffffff816bc8c2>] system_call_fastpath+0x16/0x1b >>> >> >>> >> If I terminate the program by force, then I can log in right now. >>> >> So, are there any differences between the read and the mmap function >>> >> to the wait_event_interruptible()? Why? If I want to block mmap() just >>> >> like blocking read(), what should I do? Or it is impossible? >>> >> Thanks! >>> >> >>> >> _______________________________________________ >>> >> Kernelnewbies mailing list >>> >> Kernelnewbies@kernelnewbies.org >>> >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>> > >>> > >>> >> >> >
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