Re: [PATCH] ceph: re-org copy_file_range and fix error handling paths

From: Luis Henriques
Date: Thu Feb 20 2020 - 17:36:33 EST

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On Thu, Feb 20, 2020 at 03:41:14PM -0500, Jeff Layton wrote:
> On Mon, 2020-02-17 at 12:36 +0000, Luis Henriques wrote:
> > This patch re-organizes copy_file_range, trying to fix a few issues in
> > error handling. Here's the summary:
> >
> > - Abort copy if initial do_splice_direct() returns fewer bytes than
> > requested.
> >
> > - Move the 'size' initialization (with i_size_read()) further down in the
> > code, after the initial call to do_splice_direct(). This avoids issues
> > with a possibly stale value if a manual copy is done.
> >
> > - Move the object copy loop into a separate function. This makes it
> > easier to handle errors (e.g, dirtying caps and updating the MDS
> > metadata if only some objects have been copied before an error has
> > occurred).
> >
> > - Added calls to ceph_oloc_destroy() to avoid leaking memory with src_oloc
> > and dst_oloc
> >
> > - After the object copy loop, the new file size to be reported to the MDS
> > (if there's file size change) is now the actual file size, and not the
> > size after an eventual extra manual copy.
> >
> > - Added a few dout() to show the number of bytes copied in the two manual
> > copies and in the object copy loop.
> >
> > Signed-off-by: Luis Henriques <lhenriques@xxxxxxxx>
> > ---
> > Hi!
> >
> > Initially I was going to have this patch split in a series, but then I
> > decided not to do that as this big patch allows (IMO) to better see the
> > whole picture. But please let me know if you think otherwise and I can
> > split it in a few smaller patches.
> >
> > I tried to cover all the issues that have been pointed out by Ilya, but I
> > may have missed something or, more likely, introduced new bugs ;-)
> >
> > Cheers,
> > --
> > Luis
> >
>
> Sorry for the delay in review!

No worries, I appreciate the feedback but I obviously don't expect it to
happen immediately :-)

> > fs/ceph/file.c | 169 ++++++++++++++++++++++++++++---------------------
> > 1 file changed, 96 insertions(+), 73 deletions(-)
> >
> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > index c3b8e8e0bf17..4d90a275f9a5 100644
> > --- a/fs/ceph/file.c
> > +++ b/fs/ceph/file.c
> > @@ -1931,6 +1931,71 @@ static int is_file_size_ok(struct inode *src_inode, struct inode *dst_inode,
> > return 0;
> > }
> >
> > +static ssize_t ceph_do_objects_copy(struct ceph_inode_info *src_ci, u64 *src_off,
> > + struct ceph_inode_info *dst_ci, u64 *dst_off,
> > + struct ceph_fs_client *fsc,
> > + size_t len, unsigned int flags)
> > +{
> > + struct ceph_object_locator src_oloc, dst_oloc;
> > + struct ceph_object_id src_oid, dst_oid;
> > + size_t bytes = 0;
> > + u64 src_objnum, src_objoff, dst_objnum, dst_objoff;
> > + u32 src_objlen, dst_objlen;
> > + u32 object_size = src_ci->i_layout.object_size;
> > + int ret;
> > +
> > + src_oloc.pool = src_ci->i_layout.pool_id;
> > + src_oloc.pool_ns = ceph_try_get_string(src_ci->i_layout.pool_ns);
> > + dst_oloc.pool = dst_ci->i_layout.pool_id;
> > + dst_oloc.pool_ns = ceph_try_get_string(dst_ci->i_layout.pool_ns);
> > +
> > + while (len >= object_size) {
> > + ceph_calc_file_object_mapping(&src_ci->i_layout, *src_off,
> > + object_size, &src_objnum,
> > + &src_objoff, &src_objlen);
> > + ceph_calc_file_object_mapping(&dst_ci->i_layout, *dst_off,
> > + object_size, &dst_objnum,
> > + &dst_objoff, &dst_objlen);
> > + ceph_oid_init(&src_oid);
> > + ceph_oid_printf(&src_oid, "%llx.%08llx",
> > + src_ci->i_vino.ino, src_objnum);
> > + ceph_oid_init(&dst_oid);
> > + ceph_oid_printf(&dst_oid, "%llx.%08llx",
> > + dst_ci->i_vino.ino, dst_objnum);
> > + /* Do an object remote copy */
> > + ret = ceph_osdc_copy_from(&fsc->client->osdc,
> > + src_ci->i_vino.snap, 0,
> > + &src_oid, &src_oloc,
> > + CEPH_OSD_OP_FLAG_FADVISE_SEQUENTIAL |
> > + CEPH_OSD_OP_FLAG_FADVISE_NOCACHE,
> > + &dst_oid, &dst_oloc,
> > + CEPH_OSD_OP_FLAG_FADVISE_SEQUENTIAL |
> > + CEPH_OSD_OP_FLAG_FADVISE_DONTNEED,
> > + dst_ci->i_truncate_seq,
> > + dst_ci->i_truncate_size,
> > + CEPH_OSD_COPY_FROM_FLAG_TRUNCATE_SEQ);
> > + if (ret) {
> > + if (ret == -EOPNOTSUPP) {
> > + fsc->have_copy_from2 = false;
> > + pr_notice("OSDs don't support copy-from2; disabling copy offload\n");
> > + }
> > + dout("ceph_osdc_copy_from returned %d\n", ret);
> > + if (!bytes)
> > + bytes = ret;
> > + goto out;
> > + }
> > + len -= object_size;
> > + bytes += object_size;
> > + *src_off += object_size;
> > + *dst_off += object_size;
> > + }
> > +
> > +out:
> > + ceph_oloc_destroy(&src_oloc);
> > + ceph_oloc_destroy(&dst_oloc);
> > + return bytes;
> > +}
> > +
> > static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > struct file *dst_file, loff_t dst_off,
> > size_t len, unsigned int flags)
> > @@ -1941,14 +2006,11 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > struct ceph_inode_info *dst_ci = ceph_inode(dst_inode);
> > struct ceph_cap_flush *prealloc_cf;
> > struct ceph_fs_client *src_fsc = ceph_inode_to_client(src_inode);
> > - struct ceph_object_locator src_oloc, dst_oloc;
> > - struct ceph_object_id src_oid, dst_oid;
> > - loff_t endoff = 0, size;
> > - ssize_t ret = -EIO;
> > + loff_t size;
> > + ssize_t ret = -EIO, bytes;
> > u64 src_objnum, dst_objnum, src_objoff, dst_objoff;
> > - u32 src_objlen, dst_objlen, object_size;
> > + u32 src_objlen, dst_objlen;
> > int src_got = 0, dst_got = 0, err, dirty;
> > - bool do_final_copy = false;
> >
> > if (src_inode->i_sb != dst_inode->i_sb) {
> > struct ceph_fs_client *dst_fsc = ceph_inode_to_client(dst_inode);
> > @@ -2026,22 +2088,14 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > if (ret < 0)
> > goto out_caps;
> >
> > - size = i_size_read(dst_inode);
> > - endoff = dst_off + len;
> > -
> > /* Drop dst file cached pages */
> > ret = invalidate_inode_pages2_range(dst_inode->i_mapping,
> > dst_off >> PAGE_SHIFT,
> > - endoff >> PAGE_SHIFT);
> > + (dst_off + len) >> PAGE_SHIFT);
> > if (ret < 0) {
> > dout("Failed to invalidate inode pages (%zd)\n", ret);
> > ret = 0; /* XXX */
> > }
> > - src_oloc.pool = src_ci->i_layout.pool_id;
> > - src_oloc.pool_ns = ceph_try_get_string(src_ci->i_layout.pool_ns);
> > - dst_oloc.pool = dst_ci->i_layout.pool_id;
> > - dst_oloc.pool_ns = ceph_try_get_string(dst_ci->i_layout.pool_ns);
> > -
> > ceph_calc_file_object_mapping(&src_ci->i_layout, src_off,
> > src_ci->i_layout.object_size,
> > &src_objnum, &src_objoff, &src_objlen);
> > @@ -2060,6 +2114,8 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > * starting at the src_off
> > */
> > if (src_objoff) {
> > + dout("Initial partial copy of %u bytes\n", src_objlen);
> > +
> > /*
> > * we need to temporarily drop all caps as we'll be calling
> > * {read,write}_iter, which will get caps again.
> > @@ -2067,8 +2123,9 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > put_rd_wr_caps(src_ci, src_got, dst_ci, dst_got);
> > ret = do_splice_direct(src_file, &src_off, dst_file,
> > &dst_off, src_objlen, flags);
> > - if (ret < 0) {
> > - dout("do_splice_direct returned %d\n", err);
> > + /* Abort on short copies or on error */
> > + if (ret < src_objlen) {
> > + dout("Failed partial copy (%zd)\n", ret);
> > goto out;
> > }
> > len -= ret;
> > @@ -2081,62 +2138,29 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > if (err < 0)
> > goto out_caps;
> > }
> > - object_size = src_ci->i_layout.object_size;
> > - while (len >= object_size) {
> > - ceph_calc_file_object_mapping(&src_ci->i_layout, src_off,
> > - object_size, &src_objnum,
> > - &src_objoff, &src_objlen);
> > - ceph_calc_file_object_mapping(&dst_ci->i_layout, dst_off,
> > - object_size, &dst_objnum,
> > - &dst_objoff, &dst_objlen);
> > - ceph_oid_init(&src_oid);
> > - ceph_oid_printf(&src_oid, "%llx.%08llx",
> > - src_ci->i_vino.ino, src_objnum);
> > - ceph_oid_init(&dst_oid);
> > - ceph_oid_printf(&dst_oid, "%llx.%08llx",
> > - dst_ci->i_vino.ino, dst_objnum);
> > - /* Do an object remote copy */
> > - err = ceph_osdc_copy_from(
> > - &src_fsc->client->osdc,
> > - src_ci->i_vino.snap, 0,
> > - &src_oid, &src_oloc,
> > - CEPH_OSD_OP_FLAG_FADVISE_SEQUENTIAL |
> > - CEPH_OSD_OP_FLAG_FADVISE_NOCACHE,
> > - &dst_oid, &dst_oloc,
> > - CEPH_OSD_OP_FLAG_FADVISE_SEQUENTIAL |
> > - CEPH_OSD_OP_FLAG_FADVISE_DONTNEED,
> > - dst_ci->i_truncate_seq, dst_ci->i_truncate_size,
> > - CEPH_OSD_COPY_FROM_FLAG_TRUNCATE_SEQ);
> > - if (err) {
> > - if (err == -EOPNOTSUPP) {
> > - src_fsc->have_copy_from2 = false;
> > - pr_notice("OSDs don't support copy-from2; disabling copy offload\n");
> > - }
> > - dout("ceph_osdc_copy_from returned %d\n", err);
> > - if (!ret)
> > - ret = err;
> > - goto out_caps;
> > - }
> > - len -= object_size;
> > - src_off += object_size;
> > - dst_off += object_size;
> > - ret += object_size;
> > - }
> >
> > - if (len)
> > - /* We still need one final local copy */
> > - do_final_copy = true;
> > + size = i_size_read(dst_inode);
> > + bytes = ceph_do_objects_copy(src_ci, &src_off, dst_ci, &dst_off,
> > + src_fsc, len, flags);
> > + if (bytes <= 0) {
> > + if (!ret)
> > + ret = bytes;
> > + goto out_caps;
> > + }
>
> Suppose we did the front part with do_splice_direct (ret > 0), but then
> ceph_do_objects_copy fails (bytes < 0). We "goto out_caps" but then...
>
> [...]
>
> > @@ -2152,15 +2176,14 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > out_caps:
> > put_rd_wr_caps(src_ci, src_got, dst_ci, dst_got);
> >
> > - if (do_final_copy) {
> > - err = do_splice_direct(src_file, &src_off, dst_file,
> > - &dst_off, len, flags);
> > - if (err < 0) {
> > - dout("do_splice_direct returned %d\n", err);
> > - goto out;
> > - }
> > - len -= err;
> > - ret += err;
> > + if (len && (ret >= 0)) {
>
> ...len is still positive and we do_splice_direct again (probably at the
> wrong offset?), instead of just returning a short copy. I think we
> probably want to just stop any copying if it fails at any point along
> the way, right?

Well... To be honest I deliberately wanted to try a do_splice_direct in
case the remote object copies fail (basically, reverting to something
similar to the generic_copy_file_range). Now, I've been staring at this
code for some time and I may be missing the obvious (again!). But:

- the offsets should be OK because ceph_do_objects_copy() only updates
them after each successful object copy

- len should also be consistent:
* If 'bytes' was <= 0, it should contain what was written by
do_splice_direct
* if 'bytes' was > 0, but possibly < expected (e.g. an OSD returned an
error after a few object copies), len should still be consistent

Anyway, I'm not too attached to this approach, and if you rather have this
function to return in the scenario you've described (and eventually have
the user to retry the operation) I'm OK with that.

Cheers,
--
Luís

>
> > + dout("Final partial copy of %zu bytes\n", len);
> > + bytes = do_splice_direct(src_file, &src_off, dst_file,
> > + &dst_off, len, flags);
> > + if (bytes > 0)
> > + ret += bytes;
> > + else
> > + dout("Failed partial copy (%zd)\n", bytes);
> > }
> >
> > out:
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>

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