kernel module won't link - symbol mutex_lock_nested not found

Question

I am trying to build a kernel module (stress-test tool for a hardware) for a Linux 3.10.45 on x64. So far it seemed to work fine, until adding a mutex.

I added mutex using and the functions mutex_init, mutex_lock, mutex_unlock and mutex_destroy.

Building the module yielded no errors or warnings, but when loading with 'insmod', there are error messages in dmesg:

[76603.744551] tryBlk: Unknown symbol mutex_lock_nested (err 0)
[76603.744574] tryBlk: Unknown symbol mutex_destroy (err 0)

I found a hint that with 'Unknown symbol', it sometimes helps to add the MODULE_LICENSE("GPL v2") line.

No difference.

Looking at linux/mutex.h, I found that the mutex_lock will only define to mutex_lock_nested if the symbol CONFIG_DEBUG_LOCK_ALLOC is defined. Checking this, it seems to be defined in my .config . (Cannot remember touching it. It is basically just a kernel from kernel.org, built).

Is there a problem with this? Do I need to manually add something else to my module to make it build with this debug-feature?

Tried to change include files and sequence. No difference.

System is running Debian-7 'Wheezy' x64, with kernel changed to a 3.10.45 .

The file using the mutex:

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>
#include "ring.h"




struct RingBuf
{
    unsigned char *buffer;
    unsigned int size;
    unsigned int inp,outp;
    struct mutex mtx;
};



static int _bytesavail(struct RingBuf *self);
static int _spaceavail(struct RingBuf *self);


struct RingBuf *RingBuf_init(unsigned int size)
{
  struct RingBuf *self;
    if( size<16 )size=16;
    if( size>0x10000000u )return 0;
    if( size & (size-1) )
    {
      unsigned int ns;
        // is not a power of 2.
        size = size<<1;
        while(1)
        {
            ns=size&(size-1);
            if(!ns)break;
            size=ns;
        }
    }
    self = (struct RingBuf*)vmalloc(sizeof(*self)+size);
    memset( self , 0 , sizeof(*self) );
    self->buffer = (unsigned char*)(self+1);
    self->size = size;
    self->inp = 0;
    self->outp = 0;
    mutex_init( &(self->mtx) );
    return self;
}

void RingBuf_uninit(struct RingBuf *self)
{
    if(!self)return;
    mutex_lock( &(self->mtx) );
    mutex_destroy( &(self->mtx) );
    memset( self , 0xFE , sizeof(*self) );
    vfree(self);
}

int RingBuf_add(struct RingBuf *self,const void *data,int num)
{
  int cpy;
    if(num<=0)return 0;
    mutex_lock( &(self->mtx) );
    // check amount to copy
    cpy = _spaceavail(self);
    if(cpy>num)cpy=num;
    // one part or split
    if( self->inp+cpy <= self->size )
    {
        // one chunk
        memcpy( self->buffer+self->inp , data , cpy );
    }else{
      int p1 = (self->size-self->inp);
        // wrapped
        memcpy( self->buffer+self->inp , data , p1 );
        memcpy( self->buffer , ((const unsigned char*)data)+p1 , cpy-p1 );
    }
    self->inp = (self->inp+cpy) & (self->size-1) ;
    mutex_unlock( &(self->mtx) );
    return cpy;
}

int RingBuf_get(struct RingBuf *self,void *data,int num)
{
  int cpy;
    if(num<=0)return 0;
    mutex_lock( &(self->mtx) );
    // check amount to copy
    cpy = _bytesavail(self);
    if(cpy>num)cpy=num;
    // one part or split
    if( self->outp+cpy <= self->size )
    {
        // one chunk
        memcpy( data , self->buffer+self->outp , cpy );
    }else{
      int p1 = (self->size-self->outp);
        // wrapped
        memcpy( data , self->buffer+self->outp , p1 );
        memcpy( ((unsigned char*)data)+p1 , self->buffer , cpy-p1 );
    }
    self->outp = (self->outp+cpy) & (self->size-1) ;
    mutex_unlock( &(self->mtx) );
    return cpy;
}

int RingBuf_get_user(struct RingBuf *self,void __user *data,int num)
{
  int cpy;
  int ret;
    if(num<=0)return 0;
    mutex_lock( &(self->mtx) );
    // check amount to copy
    cpy = _bytesavail(self);
    if(cpy>num)cpy=num;
    // one part or split
    if( self->outp+cpy <= self->size )
    {
        // one chunk
        ret = copy_to_user( data , self->buffer+self->outp , cpy );
    }else{
      int p1 = (self->size-self->outp);
        // wrapped
        ret = copy_to_user( data , self->buffer+self->outp , p1 );
        if(!ret)
            ret = copy_to_user( ((unsigned char*)data)+p1 , self->buffer , cpy-p1 );
    }
    if(ret)return -1;
    self->outp = (self->outp+cpy) & (self->size-1) ;
    mutex_unlock( &(self->mtx) );
    return cpy;
}

int RingBuf_numBytes(struct RingBuf *self)
{
  int result;
    mutex_lock( &(self->mtx) );
    result = _bytesavail(self);
    mutex_unlock( &(self->mtx) );
    return result;
}

static int _bytesavail(struct RingBuf *self)
{
    return (self->inp-self->outp)&(self->size-1);
}

static int _spaceavail(struct RingBuf *self)
{
    return (self->outp-self->inp-1)&(self->size-1);
}

Answer 1

I just found that it somehow depends on how I am building the module.

The mutex stuff is in another source-file (the one listed above). When I cut/paste it into the first main-source of the module, it works.

So it is a problem of how to create a module spanning several source files.

My (NOT CORRECTLY WORKING) Makefile is:

obj-m += tryBlk.o
tryBlk-objs := ring.o

It builds without warnings, but the kernel-symbols in the 'ring.o' file are not correctly found.

===============================================

I also solved the other problem now. To share, the makefile was bad.

Here the better makefile:

obj-m := tryBlk.o
tryBlk-objs := tryBlk_main.o ring.o

I also needed to rename the main part from 'tryBlk.c' to 'tryBlk_main.c'