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POkernel paging request fails in try_module_get()
 

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  1. POkernel paging request fails in try_module_get()
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    <p>The following code fails in one of my linux-kernel modules</p> <pre><code>printk("This module: %p\n",THIS_MODULE); DEBUG_USE_COUNT(p); printk("This module refcount: %d\n", module_refcount(THIS_MODULE)); DEBUG_USE_COUNT(p); if (!try_module_get(THIS_MODULE)) { printk_stderr("can't get module\n"); return -EFAULT; } </code></pre> <p>The code itself works in usual environment, but when I try to execute it in the function called from within another module, it fails with paging error. (another module is passed the pointer to the function in question during initialization) Any ideas why module can't increment its reference count being called from another module? Are there any special limitations that apply to try_get_module call?</p> <pre><code>[ 7888.065029] BUG: unable to handle kernel paging request at fa69206 8 [ 7888.067470] IP: [&lt;f926a2b6&gt;] _ZL18open_station_sharePKcP23__camac_ kernel_open_argP4file+0x84/0x8ec [camac_k0607_lsi6] //function in question, calling try_module_get() [ 7888.069014] Call Trace: [ 7888.069014] [&lt;c10ac2b7&gt;] ? __kmalloc+0x104/0x110 [ 7888.069014] [&lt;c12518f5&gt;] ? printk+0xe/0x11 [ 7888.069014] [&lt;f90fae79&gt;] ? T.633+0x46/0x4b [camac_mx] [ 7888.069014] [&lt;f90fb07e&gt;] ? camac_mx_ioctl+0x200/0x228 [camac_mx] //function of another module that calls the one in question [ 7888.069014] [&lt;c10ba415&gt;] ? vfs_ioctl+0x58/0x72 [ 7888.069014] [&lt;c10ba966&gt;] ? do_vfs_ioctl+0x492/0x4d6 [ 7888.069014] [&lt;c109007b&gt;] ? shmem_parse_options+0x167/0x281 [ 7888.069014] [&lt;c10ae69e&gt;] ? fd_install+0x1b/0x38 [ 7888.069014] [&lt;c10ae88b&gt;] ? do_sys_open+0xc8/0xdd [ 7888.069014] [&lt;c10ba9ee&gt;] ? sys_ioctl+0x44/0x64 [ 7888.069014] [&lt;c100305b&gt;] ? sysenter_do_call+0x12/0x28 </code></pre> <p>I would also be great if someone explains the garbage on the top of the printed stack. There should not be any functions in cross-module call. Top three functions on the stack are meaningless for me.</p>
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    1. COYou should probably post more details. I guess the source and a disassembly with correct addresses of _ZL18open_station_sharePKcP23__camac_ kernel_open_argP4file (is that C++ in the kernel?) would help.
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