On Thu, Sep 27, 2012 at 8:24 PM, Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> wrote: > Hi Chen, > > > 2012/09/27 19:20, Ni zhan Chen wrote: >> >> Hi Congyang, >> >> 2012/9/27 <wency@xxxxxxxxxxxxxx> >> >>> From: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx> >>> >>> When calling remove_memory_block(), the function shows following message >>> at >>> device_release(). >>> >>> Device 'memory528' does not have a release() function, it is broken and >>> must >>> be fixed. >>> >> >> What's the difference between the patch and original implemetation? > > > The implementation is for removing a memory_block. So the purpose is > same as original one. But original code is bad manner. kobject_cleanup() > is called by remove_memory_block() at last. But release function for > releasing memory_block is not registered. As a result, the kernel message > is shown. IMHO, memory_block should be release by the releae function. but your patch introduced use after free bug, if i understand correctly. See unregister_memory() function. After your patch, kobject_put() call release_memory_block() and kfree(). and then device_unregister() will touch freed memory. static void unregister_memory(struct memory_block *memory) { BUG_ON(memory->dev.bus != &memory_subsys); /* drop the ref. we got in remove_memory_block() */ kobject_put(&memory->dev.kobj); device_unregister(&memory->dev); } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>