| Message ID | alpine.LRH.2.02.2009050811200.12419@file01.intranet.prod.int.rdu2.redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] ext2: don't update mtime on COW faults | expand |
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 <mpatocka@redhat.com> > Cc: stable@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; > } >
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; }
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(-)