On Thu, Jul 25, 2019 at 11:35:21AM -0400, Vivek Goyal wrote: > On Wed, Jul 24, 2019 at 05:08:58PM -0700, Liu Bo wrote: > > On Wed, Jul 24, 2019 at 05:07:21PM -0400, Vivek Goyal wrote: > > > Do not always map a dax mapping read-write. There are use cases like > > > executing a file where we want to map file read-only. virtio-fs dir on > > > host might be backed by overlayfs. We don't want to open file read-write > > > on overlayfs otherwise it will unnecessariliy be copied-up nullyifying > > > the advantages of sharing page cache between vms for unmodified files. > > > > > > Hence, create a read-only mapping if user did not ask for writable > > > mapping. > > > Later upgrade it to read-write mapping when users requests it. > > > > > > Signed-off-by: Vivek Goyal <[email protected]> > > > --- > > > fs/fuse/file.c | 114 ++++++++++++++++++++++++++++++++++++----------- > > > fs/fuse/fuse_i.h | 3 ++ > > > 2 files changed, 91 insertions(+), 26 deletions(-) > > > > > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > > > index a2c19e4a28b5..bcd8ddcc0fdf 100644 > > > --- a/fs/fuse/file.c > > > +++ b/fs/fuse/file.c > > > @@ -265,7 +265,8 @@ static void dmap_add_to_free_pool(struct fuse_conn > > > *fc, > > > > > > /* offset passed in should be aligned to FUSE_DAX_MEM_RANGE_SZ */ > > > static int fuse_setup_one_mapping(struct inode *inode, loff_t offset, > > > - struct fuse_dax_mapping *dmap) > > > + struct fuse_dax_mapping *dmap, bool writable, > > > + bool upgrade) > > > { > > > struct fuse_conn *fc = get_fuse_conn(inode); > > > struct fuse_inode *fi = get_fuse_inode(inode); > > > @@ -283,7 +284,8 @@ static int fuse_setup_one_mapping(struct inode > > > *inode, loff_t offset, > > > inarg.moffset = dmap->window_offset; > > > inarg.len = FUSE_DAX_MEM_RANGE_SZ; > > > inarg.flags |= FUSE_SETUPMAPPING_FLAG_READ; > > > - inarg.flags |= FUSE_SETUPMAPPING_FLAG_WRITE; > > > + if (writable) > > > + inarg.flags |= FUSE_SETUPMAPPING_FLAG_WRITE; > > > args.in.h.opcode = FUSE_SETUPMAPPING; > > > args.in.h.nodeid = fi->nodeid; > > > args.in.numargs = 1; > > > @@ -296,26 +298,30 @@ static int fuse_setup_one_mapping(struct inode > > > *inode, loff_t offset, > > > return err; > > > } > > > > > > - pr_debug("fuse_setup_one_mapping() succeeded. offset=0x%llx err=%zd\n", > > > offset, err); > > > + pr_debug("fuse_setup_one_mapping() succeeded. offset=0x%llx writable=%d" > > > + " err=%zd\n", offset, writable, err); > > > > > > - /* > > > - * We don't take a refernce on inode. inode is valid right now and > > > - * when inode is going away, cleanup logic should first cleanup > > > - * dmap entries. > > > - * > > > - * TODO: Do we need to ensure that we are holding inode lock > > > - * as well. > > > - */ > > > - dmap->inode = inode; > > > - dmap->start = offset; > > > - dmap->end = offset + FUSE_DAX_MEM_RANGE_SZ - 1; > > > - /* Protected by fi->i_dmap_sem */ > > > - fuse_dax_interval_tree_insert(dmap, &fi->dmap_tree); > > > - fi->nr_dmaps++; > > > - spin_lock(&fc->lock); > > > - list_add_tail(&dmap->busy_list, &fc->busy_ranges); > > > - fc->nr_busy_ranges++; > > > - spin_unlock(&fc->lock); > > > + dmap->writable = writable; > > > + if (!upgrade) { > > > + /* > > > + * We don't take a refernce on inode. inode is valid right now > > > + * and when inode is going away, cleanup logic should first > > > + * cleanup dmap entries. > > > + * > > > + * TODO: Do we need to ensure that we are holding inode lock > > > + * as well. > > > + */ > > > + dmap->inode = inode; > > > + dmap->start = offset; > > > + dmap->end = offset + FUSE_DAX_MEM_RANGE_SZ - 1; > > > + /* Protected by fi->i_dmap_sem */ > > > + fuse_dax_interval_tree_insert(dmap, &fi->dmap_tree); > > > + fi->nr_dmaps++; > > > + spin_lock(&fc->lock); > > > + list_add_tail(&dmap->busy_list, &fc->busy_ranges); > > > + fc->nr_busy_ranges++; > > > + spin_unlock(&fc->lock); > > > + } > > > return 0; > > > } > > > > > > @@ -1890,6 +1896,7 @@ static int iomap_begin_setup_new_mapping(struct > > > inode *inode, loff_t pos, > > > struct fuse_conn *fc = get_fuse_conn(inode); > > > struct fuse_dax_mapping *dmap, *alloc_dmap = NULL; > > > int ret; > > > + bool writable = flags & IOMAP_WRITE; > > > > > > /* Can't do reclaim in fault path yet due to lock ordering. > > > * Read path takes shared inode lock and that's not sufficient > > > @@ -1930,10 +1937,11 @@ static int iomap_begin_setup_new_mapping(struct > > > inode *inode, loff_t pos, > > > > > > /* Setup one mapping */ > > > ret = fuse_setup_one_mapping(inode, > > > - ALIGN_DOWN(pos, FUSE_DAX_MEM_RANGE_SZ), alloc_dmap); > > > + ALIGN_DOWN(pos, FUSE_DAX_MEM_RANGE_SZ), > > > + alloc_dmap, writable, false); > > > if (ret < 0) { > > > printk("fuse_setup_one_mapping() failed. err=%d" > > > - " pos=0x%llx\n", ret, pos); > > > + " pos=0x%llx, writable=%d\n", ret, pos, writable); > > > dmap_add_to_free_pool(fc, alloc_dmap); > > > up_write(&fi->i_dmap_sem); > > > return ret; > > > @@ -1943,6 +1951,45 @@ static int iomap_begin_setup_new_mapping(struct > > > inode *inode, loff_t pos, > > > return 0; > > > } > > > > > > +static int iomap_begin_upgrade_mapping(struct inode *inode, loff_t pos, > > > + loff_t length, unsigned flags, > > > + struct iomap *iomap) > > > +{ > > > + struct fuse_inode *fi = get_fuse_inode(inode); > > > + struct fuse_dax_mapping *dmap; > > > + int ret; > > > + > > > + /* > > > + * Take exclusive lock so that only one caller can try to setup > > > + * mapping and others wait. > > > + */ > > > + down_write(&fi->i_dmap_sem); > > > + dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, pos, pos); > > > + > > > + /* We are holding either inode lock or i_mmap_sem, and that should > > > + * ensure that dmap can't reclaimed or truncated and it should still > > > + * be there in tree despite the fact we dropped and re-acquired the > > > + * lock. > > > + */ > > > + if (WARN_ON(!dmap)) > > > + return -EIO; > > > > up_write() is missed here. > > Good catch. Will fix it. > > > > > And I posted a similar patch[1] but with inode_lock being dropped in > > mind, anything wrong with that patch? > > It was an old posting so did not pay much attention to it. Looking at > it now and few things I notice. > > - That patch will allocate and possibly wait for memory range and free > it up when upgrading from read-only to read-write. That's not required. >
What I was trying to say is that the above assumption about "dmap is still in tree despite dropping-acquiring lock" is doubtful if inode lock is not held by reclaim code. There is a window between dropping and reacquiring lock, if it gets reclaimed, we're supposed to continue on the allocation path. > - dmap->flags is not required at this point of time. If we add more > states later, we can convert it to a flag. > > - Code structure seems little simpler in this patch (in > fuse_iomap_begin()). I like the cleanups. thanks, -liubo > > W.r.t dropping inode lock, I think we should still be able to do with this > patch and take reference on dmap under shared lock. And drop that > reference later. Taking that reference should make sure dmap will not > be reclaimed when we don't have i_dmap_sem. And truncate/punch_hole > can't reclaim anyway because of inode_lock/i_mmap_sem lock. > > Thanks > Vivek
