[PATCH v3 1/4] ceph: do not propagate page array emplacement errors as batch errors

[PATCH v3 1/4] ceph: do not propagate page array emplacement errors as batch errors

[Sam Edwards]

When fscrypt is enabled, move_dirty_folio_in_page_array() may fail
because it needs to allocate bounce buffers to store the encrypted
versions of each folio. Each folio beyond the first allocates its bounce
buffer with GFP_NOWAIT. Failures are common (and expected) under this
allocation mode; they should flush (not abort) the batch.

However, ceph_process_folio_batch() uses the same `rc` variable for its
own return code and for capturing the return codes of its routine calls;
failing to reset `rc` back to 0 results in the error being propagated
out to the main writeback loop, which cannot actually tolerate any
errors here: once `ceph_wbc.pages` is allocated, it must be passed to
ceph_submit_write() to be freed. If it survives until the next iteration
(e.g. due to the goto being followed), ceph_allocate_page_array()'s
BUG_ON() will oops the worker.

Note that this failure mode is currently masked due to another bug
(addressed next in this series) that prevents multiple encrypted folios
from being selected for the same write.

For now, just reset `rc` when redirtying the folio to prevent errors in
move_dirty_folio_in_page_array() from propagating. Note that
move_dirty_folio_in_page_array() is careful never to return errors on
the first folio, so there is no need to check for that. After this
change, ceph_process_folio_batch() no longer returns errors; its only
remaining failure indicator is `locked_pages == 0`, which the caller
already handles correctly.

Fixes: ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method")
Cc: stable@vger.kernel.org
Signed-off-by: Sam Edwards <CFSworks@gmail.com>
---
 fs/ceph/addr.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 63b75d214210..3462df35d245 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -1369,6 +1369,7 @@ int ceph_process_folio_batch(struct address_space *mapping,
 		rc = move_dirty_folio_in_page_array(mapping, wbc, ceph_wbc,
 				folio);
 		if (rc) {
+			rc = 0;
 			folio_redirty_for_writepage(wbc, folio);
 			folio_unlock(folio);
 			break;
-- 
2.52.0

[PATCH v3 2/4] ceph: fix write storm on fscrypted files

[Sam Edwards]

CephFS stores file data across multiple RADOS objects. An object is the
atomic unit of storage, so the writeback code must clean only folios
that belong to the same object with each OSD request.

CephFS also supports RAID0-style striping of file contents: if enabled,
each object stores multiple unbroken "stripe units" covering different
portions of the file; if disabled, a "stripe unit" is simply the whole
object. The stripe unit is (usually) reported as the inode's block size.

Though the writeback logic could, in principle, lock all dirty folios
belonging to the same object, its current design is to lock only a
single stripe unit at a time. Ever since this code was first written,
it has determined this size by checking the inode's block size.
However, the relatively-new fscrypt support needed to reduce the block
size for encrypted inodes to the crypto block size (see 'fixes' commit),
which causes an unnecessarily high number of write operations (~1024x as
many, with 4MiB objects) and correspondingly degraded performance.

Fix this (and clarify intent) by using i_layout.stripe_unit directly in
ceph_define_write_size() so that encrypted inodes are written back with
the same number of operations as if they were unencrypted.

This patch depends on the preceding commit ("ceph: do not propagate page
array emplacement errors as batch errors") for correctness. While it
applies cleanly on its own, applying it alone will introduce a
regression. This dependency is only relevant for kernels where
ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method") has
been applied; stable kernels without that commit are unaffected.

Fixes: 94af0470924c ("ceph: add some fscrypt guardrails")
Cc: stable@vger.kernel.org
Signed-off-by: Sam Edwards <CFSworks@gmail.com>
---
 fs/ceph/addr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 3462df35d245..39064893f35b 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -1000,7 +1000,8 @@ unsigned int ceph_define_write_size(struct address_space *mapping)
 {
 	struct inode *inode = mapping->host;
 	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
-	unsigned int wsize = i_blocksize(inode);
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	unsigned int wsize = ci->i_layout.stripe_unit;
 
 	if (fsc->mount_options->wsize < wsize)
 		wsize = fsc->mount_options->wsize;
-- 
2.52.0