On Sat 05-09-20 08:12:01, Mikulas Patocka wrote:
> 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 <mpato...@redhat.com>
> Cc: sta...@vger.kernel.org
Thanks. Good spotting! Linus has already merged this so nothing more to do
here.
Honza
>
> ---
> 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;
> }
>
--
Jan Kara <j...@suse.com>
SUSE Labs, CR
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