On Mon, Aug 29, 2011 at 05:05:47PM +0200, Jan Altenberg wrote: [Since we got no reply on linux-mm, I added lkml and Andrew to Cc: (mm doesn't seem to have a maintainer...)] > Hi, > > I'm currently analysing a problem similar to some mmap() issue reported > in the past: https://lkml.org/lkml/2010/7/11/140 The arch there was microblaze, and you are working on arm. That means the problem appears on at least to archs. > > 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); >From my point of view (I've got Jan's full test case code), this is a completely correct UIO use case. > > 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) Quite strange that memory that could be mapped with mmap() cannot be unmapped with munmap(). > > This happens for every page except the first one. ...which is the next strange thing. > 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 pages are mapped when you access them through the UIO core page fault handler. > 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. That is more than strange, that points to some things going really wrong. > > Any idea what might be wrong here? Am I missing something obvious? (I've > prepared some brown paperbags for that case ;-)) > > Thanks, > Jan > Thanks, Jan, for reporting this! Hans -- 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>