Commit b17164e2 authored Sep 05, 2020 by Mikulas Patocka Committed by Linus Torvalds Sep 05, 2020

xfs: 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 xfs 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 xfs 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
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1ef6ea0e

fs/xfs/xfs_file.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -1223,6 +1223,14 @@ __xfs_filemap_fault(
		return ret;
		}

		static inline bool
		xfs_is_write_fault(
		struct vm_fault *vmf)
		{
		return (vmf->flags & FAULT_FLAG_WRITE) &&
		(vmf->vma->vm_flags & VM_SHARED);
		}

		static vm_fault_t
		xfs_filemap_fault(
		struct vm_fault *vmf)
		@@ -1230,7 +1238,7 @@ xfs_filemap_fault(
		/* DAX can shortcut the normal fault path on write faults! */
		return __xfs_filemap_fault(vmf, PE_SIZE_PTE,
		IS_DAX(file_inode(vmf->vma->vm_file)) &&
		(vmf->flags & FAULT_FLAG_WRITE));
		xfs_is_write_fault(vmf));
		}

		static vm_fault_t
		@@ -1243,7 +1251,7 @@ xfs_filemap_huge_fault(

		/* DAX can shortcut the normal fault path on write faults! */
		return __xfs_filemap_fault(vmf, pe_size,
		(vmf->flags & FAULT_FLAG_WRITE));
		xfs_is_write_fault(vmf));
		}

		static vm_fault_t

Admin message