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Subject[PATCH v3 1/2] netfs: do not unlock and put the folio twice
Date
From: Xiubo Li <xiubli@redhat.com>

check_write_begin() will unlock and put the folio when return
non-zero. So we should avoid unlocking and putting it twice in
netfs layer.

At the same time pass a **folio to check_write_begin(), in which
the folio should be cleared after being put.

URL: https://tracker.ceph.com/issues/56423
Signed-off-by: Xiubo Li <xiubli@redhat.com>
---
fs/afs/file.c | 2 +-
fs/ceph/addr.c | 11 ++++++-----
fs/netfs/buffered_read.c | 18 ++++++++++--------
include/linux/netfs.h | 2 +-
4 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 42118a4f3383..afacce797fb9 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -375,7 +375,7 @@ static int afs_begin_cache_operation(struct netfs_io_request *rreq)
}

static int afs_check_write_begin(struct file *file, loff_t pos, unsigned len,
- struct folio *folio, void **_fsdata)
+ struct folio **folio, void **_fsdata)
{
struct afs_vnode *vnode = AFS_FS_I(file_inode(file));

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 8095fc47230e..cf909b08907f 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -63,7 +63,7 @@
(CONGESTION_ON_THRESH(congestion_kb) >> 2))

static int ceph_netfs_check_write_begin(struct file *file, loff_t pos, unsigned int len,
- struct folio *folio, void **_fsdata);
+ struct folio **folio, void **_fsdata);

static inline struct ceph_snap_context *page_snap_context(struct page *page)
{
@@ -1280,18 +1280,19 @@ ceph_find_incompatible(struct page *page)
}

static int ceph_netfs_check_write_begin(struct file *file, loff_t pos, unsigned int len,
- struct folio *folio, void **_fsdata)
+ struct folio **folio, void **_fsdata)
{
struct inode *inode = file_inode(file);
struct ceph_inode_info *ci = ceph_inode(inode);
struct ceph_snap_context *snapc;

- snapc = ceph_find_incompatible(folio_page(folio, 0));
+ snapc = ceph_find_incompatible(folio_page(*folio, 0));
if (snapc) {
int r;

- folio_unlock(folio);
- folio_put(folio);
+ folio_unlock(*folio);
+ folio_put(*folio);
+ *folio = NULL;
if (IS_ERR(snapc))
return PTR_ERR(snapc);

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index 42f892c5712e..308c2ad4da8e 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -319,8 +319,8 @@ static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
* conflicting writes once the folio is grabbed and locked. It is passed a
* pointer to the fsdata cookie that gets returned to the VM to be passed to
* write_end. It is permitted to sleep. It should return 0 if the request
- * should go ahead; unlock the folio and return -EAGAIN to cause the folio to
- * be regot; or return an error.
+ * should go ahead; otherwise unlock, put and clear the folio and then return
+ * an error, -EAGAIN will cause the folio to be regot.
*
* The calling netfs must initialise a netfs context contiguous to the vfs
* inode before calling this.
@@ -348,13 +348,14 @@ int netfs_write_begin(struct netfs_inode *ctx,

if (ctx->ops->check_write_begin) {
/* Allow the netfs (eg. ceph) to flush conflicts. */
- ret = ctx->ops->check_write_begin(file, pos, len, folio, _fsdata);
+ ret = ctx->ops->check_write_begin(file, pos, len, &folio, _fsdata);
if (ret < 0) {
trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
if (ret == -EAGAIN)
goto retry;
- goto error;
+ goto error_unlocked;
}
+ BUG_ON(!folio);
}

if (folio_test_uptodate(folio))
@@ -375,7 +376,7 @@ int netfs_write_begin(struct netfs_inode *ctx,
NETFS_READ_FOR_WRITE);
if (IS_ERR(rreq)) {
ret = PTR_ERR(rreq);
- goto error;
+ goto error_locked;
}
rreq->no_unlock_folio = folio_index(folio);
__set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
@@ -402,12 +403,12 @@ int netfs_write_begin(struct netfs_inode *ctx,

ret = netfs_begin_read(rreq, true);
if (ret < 0)
- goto error;
+ goto error_locked;

have_folio:
ret = folio_wait_fscache_killable(folio);
if (ret < 0)
- goto error;
+ goto error_locked;
have_folio_no_wait:
*_folio = folio;
_leave(" = 0");
@@ -415,9 +416,10 @@ int netfs_write_begin(struct netfs_inode *ctx,

error_put:
netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
-error:
+error_locked:
folio_unlock(folio);
folio_put(folio);
+error_unlocked:
_leave(" = %d", ret);
return ret;
}
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 1773e5df8e65..88c4eb85c6f7 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -214,7 +214,7 @@ struct netfs_request_ops {
void (*issue_read)(struct netfs_io_subrequest *subreq);
bool (*is_still_valid)(struct netfs_io_request *rreq);
int (*check_write_begin)(struct file *file, loff_t pos, unsigned len,
- struct folio *folio, void **_fsdata);
+ struct folio **folio, void **_fsdata);
void (*done)(struct netfs_io_request *rreq);
};

--
2.36.0.rc1
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