lkml.org 
[lkml]   [2020]   [Sep]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH 1/2] ext2: don't update mtime on COW faults
    When running in a dax mode, if the user maps a page with MAP_PRIVATE and
    PROT_WRITE, the ext2 filesystem would incorrectly update ctime and mtime
    when the user hits a COW fault.

    This breaks building of the Linux kernel.
    How to reproduce:
    1. extract the Linux kernel tree on dax-mounted ext2 filesystem
    2. run make clean
    3. run make -j12
    4. run make -j12
    - at step 4, make would incorrectly rebuild the whole kernel (although it
    was already built in step 3).

    The reason for the breakage is that almost all object files depend on
    objtool. When we run objtool, it takes COW page fault on its .data
    section, and these faults will incorrectly update the timestamp of the
    objtool binary. The updated timestamp causes make to rebuild the whole
    tree.

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
    Cc: stable@vger.kernel.org

    ---
    fs/ext2/file.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    Index: linux-2.6/fs/ext2/file.c
    ===================================================================
    --- linux-2.6.orig/fs/ext2/file.c 2020-09-05 10:01:41.000000000 +0200
    +++ linux-2.6/fs/ext2/file.c 2020-09-05 13:09:50.000000000 +0200
    @@ -93,8 +93,10 @@ static vm_fault_t ext2_dax_fault(struct
    struct inode *inode = file_inode(vmf->vma->vm_file);
    struct ext2_inode_info *ei = EXT2_I(inode);
    vm_fault_t ret;
    + bool write = (vmf->flags & FAULT_FLAG_WRITE) &&
    + (vmf->vma->vm_flags & VM_SHARED);

    - if (vmf->flags & FAULT_FLAG_WRITE) {
    + if (write) {
    sb_start_pagefault(inode->i_sb);
    file_update_time(vmf->vma->vm_file);
    }
    @@ -103,7 +105,7 @@ static vm_fault_t ext2_dax_fault(struct
    ret = dax_iomap_fault(vmf, PE_SIZE_PTE, NULL, NULL, &ext2_iomap_ops);

    up_read(&ei->dax_sem);
    - if (vmf->flags & FAULT_FLAG_WRITE)
    + if (write)
    sb_end_pagefault(inode->i_sb);
    return ret;
    }
    \
     
     \ /
      Last update: 2020-09-05 14:12    [W:2.106 / U:0.112 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site