From 5c282551d152610f982591a7f0b97ef1b4b7d21f Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Sat, 5 Sep 2020 08:13:02 -0400 Subject: [PATCH] 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 Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds --- fs/xfs/xfs_file.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index c31cd3be9fb24..a29f78a663ca5 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -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 -- 2.39.5