Hi, I'm currently analysing a problem similar to some mmap() issue reported in the past: https://lkml.org/lkml/2010/7/11/140 So, what I'm trying to do is mapping some physically continuous memory (allocated by kmalloc) to userspace, using a trivial UIO driver (the idea is that a device can directly DMA to that buffer): [...] #define MEM_SIZE (4 * PAGE_SIZE) addr = kmalloc(MEM_SIZE, GFP_KERNEL) [...] info.mem[0].addr = (unsigned long) addr; info.mem[0].internal_addr = addr; info.mem[0].size = MEM_SIZE; info.mem[0].memtype = UIO_MEM_LOGICAL; [...] ret = uio_register_device(&pdev->dev, &info); Userspace maps that memory range and writes its contents to a file: [...] fd = open("/dev/uio0", O_RDWR); if (fd < 0) { perror("Can't open UIO device\n"); exit(1); } mem_map = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); if(mem_map == MAP_FAILED) { perror("Can't map UIO memory\n"); ret = -ENOMEM; goto out_file; } [...] bytes_written = write(fd_file, mem_map, MAP_SIZE) [...] munmap(mem_map); So, what happens is (I'm currently testing with 3.0.3 on ARM VersatilePB): When I do the munmap(), I run into the following error: BUG: Bad page state in process uio_test pfn:078ed page:c0409154 count:0 mapcount:0 mapping: (null) index:0x0 page flags: 0x284(referenced|slab|arch_1) [<c0033e50>] (unwind_backtrace+0x0/0xe4) from [<c0079938>] (bad_page+0xcc/0xf8) [<c0079938>] (bad_page+0xcc/0xf8) from [<c007a5f0>] (free_pages_prepare+0x6c/0xcc) [<c007a5f0>] (free_pages_prepare+0x6c/0xcc) from [<c007a778>] (free_hot_cold_page+0x20/0x18c) [<c007a778>] (free_hot_cold_page+0x20/0x18c) from [<c008ccb4>] (unmap_vmas+0x338/0x564) [<c008ccb4>] (unmap_vmas+0x338/0x564) from [<c008f0f4>] (unmap_region+0xa4/0x1e0) [<c008f0f4>] (unmap_region+0xa4/0x1e0) from [<c0090428>] (do_munmap+0x20c/0x274) [<c0090428>] (do_munmap+0x20c/0x274) from [<c00904cc>] (sys_munmap+0x3c/0x50) [<c00904cc>] (sys_munmap+0x3c/0x50) from [<c002e680>] (ret_fast_syscall+0x0/0x2c) Disabling lock debugging due to kernel taint BUG: Bad page state in process uio_test pfn:078ee page:c0409178 count:0 mapcount:0 mapping: (null) index:0x0 page flags: 0x284(referenced|slab|arch_1) [<c0033e50>] (unwind_backtrace+0x0/0xe4) from [<c0079938>] (bad_page+0xcc/0xf8) [<c0079938>] (bad_page+0xcc/0xf8) from [<c007a5f0>] (free_pages_prepare+0x6c/0xcc) [<c007a5f0>] (free_pages_prepare+0x6c/0xcc) from [<c007a778>] (free_hot_cold_page+0x20/0x18c) [<c007a778>] (free_hot_cold_page+0x20/0x18c) from [<c008ccb4>] (unmap_vmas+0x338/0x564) [<c008ccb4>] (unmap_vmas+0x338/0x564) from [<c008f0f4>] (unmap_region+0xa4/0x1e0) [<c008f0f4>] (unmap_region+0xa4/0x1e0) from [<c0090428>] (do_munmap+0x20c/0x274) [<c0090428>] (do_munmap+0x20c/0x274) from [<c00904cc>] (sys_munmap+0x3c/0x50) [<c00904cc>] (sys_munmap+0x3c/0x50) from [<c002e680>] (ret_fast_syscall+0x0/0x2c) BUG: Bad page state in process uio_test pfn:078ef page:c040919c count:0 mapcount:0 mapping: (null) index:0x0 page flags: 0x284(referenced|slab|arch_1) [<c0033e50>] (unwind_backtrace+0x0/0xe4) from [<c0079938>] (bad_page+0xcc/0xf8) [<c0079938>] (bad_page+0xcc/0xf8) from [<c007a5f0>] (free_pages_prepare+0x6c/0xcc) [<c007a5f0>] (free_pages_prepare+0x6c/0xcc) from [<c007a778>] (free_hot_cold_page+0x20/0x18c) [<c007a778>] (free_hot_cold_page+0x20/0x18c) from [<c008ccb4>] (unmap_vmas+0x338/0x564) [<c008ccb4>] (unmap_vmas+0x338/0x564) from [<c008f0f4>] (unmap_region+0xa4/0x1e0) [<c008f0f4>] (unmap_region+0xa4/0x1e0) from [<c0090428>] (do_munmap+0x20c/0x274) [<c0090428>] (do_munmap+0x20c/0x274) from [<c00904cc>] (sys_munmap+0x3c/0x50) [<c00904cc>] (sys_munmap+0x3c/0x50) from [<c002e680>] (ret_fast_syscall+0x0/0x2c) This happens for every page except the first one. If I change the code and just touch the first page, everything's working fine. As soon as I touch one of the other pages, I can see the "bad page state error" for that page. The kernel is currently built using CONFIG_SLAB (my .config is based on the versatile_defconfig); if I change to CONFIG_SLUB, munmap() seems to be happy and I can't see the "bad page state" error. Any idea what might be wrong here? Am I missing something obvious? (I've prepared some brown paperbags for that case ;-)) Thanks, Jan -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>