[PATCH 03/29] xfs: add NOWAIT semantics for readdir

Hao Xu
2023-08-25T13:56:31Z

Implement NOWAIT semantics for readdir. Return EAGAIN error to the
caller if it would block, like failing to get locks, or going to
do IO.

Co-developed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Hao Xu <howeyxu@tencent.com>
[fixes deadlock issue, tweak code style]
---
fs/xfs/libxfs/xfs_da_btree.c | 16 +++++++++++
fs/xfs/libxfs/xfs_da_btree.h | 1 +
fs/xfs/libxfs/xfs_dir2_block.c | 7 ++---
fs/xfs/libxfs/xfs_dir2_priv.h | 2 +-
fs/xfs/scrub/dir.c | 2 +-
fs/xfs/scrub/readdir.c | 2 +-
fs/xfs/xfs_dir2_readdir.c | 49 ++++++++++++++++++++++++++--------
fs/xfs/xfs_inode.c | 27 +++++++++++++++++++
fs/xfs/xfs_inode.h | 17 +++++++-----
9 files changed, 99 insertions(+), 24 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
index e576560b46e9..2638eb37bc77 100644
--- a/fs/xfs/libxfs/xfs_da_btree.c
+++ b/fs/xfs/libxfs/xfs_da_btree.c
@@ -2643,16 +2643,32 @@ xfs_da_read_buf(
struct xfs_buf_map map, *mapp = &map;
int nmap = 1;
int error;
+ int buf_flags = 0;

*bpp = NULL;
error = xfs_dabuf_map(dp, bno, flags, whichfork, &mapp, &nmap);
if (error || !nmap)
goto out_free;

+ /*
+ * NOWAIT semantics mean we don't wait on the buffer lock nor do we
+ * issue IO for this buffer if it is not already in memory. Caller will
+ * retry. This will return -EAGAIN if the buffer is in memory and cannot
+ * be locked, and no buffer and no error if it isn't in memory. We
+ * translate both of those into a return state of -EAGAIN and *bpp =
+ * NULL.
+ */
+ if (flags & XFS_DABUF_NOWAIT)
+ buf_flags |= XBF_NOWAIT | XBF_INCORE;
error = xfs_trans_read_buf_map(mp, tp, mp->m_ddev_targp, mapp, nmap, 0,
&bp, ops);
if (error)
goto out_free;
+ if (!bp) {
+ ASSERT(flags & XFS_DABUF_NOWAIT);
+ error = -EAGAIN;
+ goto out_free;
+ }

if (whichfork == XFS_ATTR_FORK)
xfs_buf_set_ref(bp, XFS_ATTR_BTREE_REF);
diff --git a/fs/xfs/libxfs/xfs_da_btree.h b/fs/xfs/libxfs/xfs_da_btree.h
index ffa3df5b2893..32e7b1cca402 100644
--- a/fs/xfs/libxfs/xfs_da_btree.h
+++ b/fs/xfs/libxfs/xfs_da_btree.h
@@ -205,6 +205,7 @@ int xfs_da3_node_read_mapped(struct xfs_trans *tp, struct xfs_inode *dp,
*/

#define XFS_DABUF_MAP_HOLE_OK (1u << 0)
+#define XFS_DABUF_NOWAIT (1u << 1)

int xfs_da_grow_inode(xfs_da_args_t *args, xfs_dablk_t *new_blkno);
int xfs_da_grow_inode_int(struct xfs_da_args *args, xfs_fileoff_t *bno,
diff --git a/fs/xfs/libxfs/xfs_dir2_block.c b/fs/xfs/libxfs/xfs_dir2_block.c
index 00f960a703b2..59b24a594add 100644
--- a/fs/xfs/libxfs/xfs_dir2_block.c
+++ b/fs/xfs/libxfs/xfs_dir2_block.c
@@ -135,13 +135,14 @@ int
xfs_dir3_block_read(
struct xfs_trans *tp,
struct xfs_inode *dp,
+ unsigned int flags,
struct xfs_buf **bpp)
{
struct xfs_mount *mp = dp->i_mount;
xfs_failaddr_t fa;
int err;

- err = xfs_da_read_buf(tp, dp, mp->m_dir_geo->datablk, 0, bpp,
+ err = xfs_da_read_buf(tp, dp, mp->m_dir_geo->datablk, flags, bpp,
XFS_DATA_FORK, &xfs_dir3_block_buf_ops);
if (err || !*bpp)
return err;
@@ -380,7 +381,7 @@ xfs_dir2_block_addname(
tp = args->trans;

/* Read the (one and only) directory block into bp. */
- error = xfs_dir3_block_read(tp, dp, &bp);
+ error = xfs_dir3_block_read(tp, dp, 0, &bp);
if (error)
return error;

@@ -695,7 +696,7 @@ xfs_dir2_block_lookup_int(
dp = args->dp;
tp = args->trans;

- error = xfs_dir3_block_read(tp, dp, &bp);
+ error = xfs_dir3_block_read(tp, dp, 0, &bp);
if (error)
return error;

diff --git a/fs/xfs/libxfs/xfs_dir2_priv.h b/fs/xfs/libxfs/xfs_dir2_priv.h
index 7404a9ff1a92..7d4cf8a0f15b 100644
--- a/fs/xfs/libxfs/xfs_dir2_priv.h
+++ b/fs/xfs/libxfs/xfs_dir2_priv.h
@@ -51,7 +51,7 @@ extern int xfs_dir_cilookup_result(struct xfs_da_args *args,

/* xfs_dir2_block.c */
extern int xfs_dir3_block_read(struct xfs_trans *tp, struct xfs_inode *dp,
- struct xfs_buf **bpp);
+ unsigned int flags, struct xfs_buf **bpp);
extern int xfs_dir2_block_addname(struct xfs_da_args *args);
extern int xfs_dir2_block_lookup(struct xfs_da_args *args);
extern int xfs_dir2_block_removename(struct xfs_da_args *args);
diff --git a/fs/xfs/scrub/dir.c b/fs/xfs/scrub/dir.c
index 0b491784b759..5cc51f201bd7 100644
--- a/fs/xfs/scrub/dir.c
+++ b/fs/xfs/scrub/dir.c
@@ -313,7 +313,7 @@ xchk_directory_data_bestfree(
/* dir block format */
if (lblk != XFS_B_TO_FSBT(mp, XFS_DIR2_DATA_OFFSET))
xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, lblk);
- error = xfs_dir3_block_read(sc->tp, sc->ip, &bp);
+ error = xfs_dir3_block_read(sc->tp, sc->ip, 0, &bp);
} else {
/* dir data format */
error = xfs_dir3_data_read(sc->tp, sc->ip, lblk, 0, &bp);
diff --git a/fs/xfs/scrub/readdir.c b/fs/xfs/scrub/readdir.c
index e51c1544be63..f0a727311632 100644
--- a/fs/xfs/scrub/readdir.c
+++ b/fs/xfs/scrub/readdir.c
@@ -101,7 +101,7 @@ xchk_dir_walk_block(
unsigned int off, next_off, end;
int error;

- error = xfs_dir3_block_read(sc->tp, dp, &bp);
+ error = xfs_dir3_block_read(sc->tp, dp, 0, &bp);
if (error)
return error;

diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
index 9f3ceb461515..dcdbd26e0402 100644
--- a/fs/xfs/xfs_dir2_readdir.c
+++ b/fs/xfs/xfs_dir2_readdir.c
@@ -149,6 +149,7 @@ xfs_dir2_block_getdents(
struct xfs_da_geometry *geo = args->geo;
unsigned int offset, next_offset;
unsigned int end;
+ unsigned int flags = 0;

/*
* If the block number in the offset is out of range, we're done.
@@ -156,7 +157,9 @@ xfs_dir2_block_getdents(
if (xfs_dir2_dataptr_to_db(geo, ctx->pos) > geo->datablk)
return 0;

- error = xfs_dir3_block_read(args->trans, dp, &bp);
+ if (ctx->flags & DIR_CONTEXT_F_NOWAIT)
+ flags |= XFS_DABUF_NOWAIT;
+ error = xfs_dir3_block_read(args->trans, dp, flags, &bp);
if (error)
return error;

@@ -240,6 +243,7 @@ xfs_dir2_block_getdents(
STATIC int
xfs_dir2_leaf_readbuf(
struct xfs_da_args *args,
+ struct dir_context *ctx,
size_t bufsize,
xfs_dir2_off_t *cur_off,
xfs_dablk_t *ra_blk,
@@ -258,10 +262,15 @@ xfs_dir2_leaf_readbuf(
struct xfs_iext_cursor icur;
int ra_want;
int error = 0;
-
- error = xfs_iread_extents(args->trans, dp, XFS_DATA_FORK);
- if (error)
- goto out;
+ unsigned int flags = 0;
+
+ if (ctx->flags & DIR_CONTEXT_F_NOWAIT) {
+ flags |= XFS_DABUF_NOWAIT;
+ } else {
+ error = xfs_iread_extents(args->trans, dp, XFS_DATA_FORK);
+ if (error)
+ goto out;
+ }

/*
* Look for mapped directory blocks at or above the current offset.
@@ -280,7 +289,7 @@ xfs_dir2_leaf_readbuf(
new_off = xfs_dir2_da_to_byte(geo, map.br_startoff);
if (new_off > *cur_off)
*cur_off = new_off;
- error = xfs_dir3_data_read(args->trans, dp, map.br_startoff, 0, &bp);
+ error = xfs_dir3_data_read(args->trans, dp, map.br_startoff, flags, &bp);
if (error)
goto out;

@@ -360,6 +369,7 @@ xfs_dir2_leaf_getdents(
int byteoff; /* offset in current block */
unsigned int offset = 0;
int error = 0; /* error return value */
+ int written = 0;

/*
* If the offset is at or past the largest allowed value,
@@ -391,10 +401,17 @@ xfs_dir2_leaf_getdents(
bp = NULL;
}

- if (*lock_mode == 0)
- *lock_mode = xfs_ilock_data_map_shared(dp);
- error = xfs_dir2_leaf_readbuf(args, bufsize, &curoff,
- &rablk, &bp);
+ if (*lock_mode == 0) {
+ *lock_mode =
+ xfs_ilock_data_map_shared_generic(dp,
+ ctx->flags & DIR_CONTEXT_F_NOWAIT);
+ if (!*lock_mode) {
+ error = -EAGAIN;
+ break;
+ }
+ }
+ error = xfs_dir2_leaf_readbuf(args, ctx, bufsize,
+ &curoff, &rablk, &bp);
if (error || !bp)
break;

@@ -479,6 +496,7 @@ xfs_dir2_leaf_getdents(
*/
offset += length;
curoff += length;
+ written += length;
/* bufsize may have just been a guess; don't go negative */
bufsize = bufsize > length ? bufsize - length : 0;
}
@@ -492,6 +510,8 @@ xfs_dir2_leaf_getdents(
ctx->pos = xfs_dir2_byte_to_dataptr(curoff) & 0x7fffffff;
if (bp)
xfs_trans_brelse(args->trans, bp);
+ if (error == -EAGAIN && written > 0)
+ error = 0;
return error;
}

@@ -514,6 +534,7 @@ xfs_readdir(
unsigned int lock_mode;
bool isblock;
int error;
+ bool nowait;

trace_xfs_readdir(dp);

@@ -531,7 +552,11 @@ xfs_readdir(
if (dp->i_df.if_format == XFS_DINODE_FMT_LOCAL)
return xfs_dir2_sf_getdents(&args, ctx);

- lock_mode = xfs_ilock_data_map_shared(dp);
+ nowait = ctx->flags & DIR_CONTEXT_F_NOWAIT;
+ lock_mode = xfs_ilock_data_map_shared_generic(dp, nowait);
+ if (!lock_mode)
+ return -EAGAIN;
+
error = xfs_dir2_isblock(&args, &isblock);
if (error)
goto out_unlock;
@@ -546,5 +571,7 @@ xfs_readdir(
out_unlock:
if (lock_mode)
xfs_iunlock(dp, lock_mode);
+ if (error == -EAGAIN)
+ ASSERT(nowait);
return error;
}
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 9e62cc500140..d088f7d0c23a 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -120,6 +120,33 @@ xfs_ilock_data_map_shared(
return lock_mode;
}

+/*
+ * Similar to xfs_ilock_data_map_shared(), except that it will only try to lock
+ * the inode in shared mode if the extents are already in memory. If it fails to
+ * get the lock or has to do IO to read the extent list, fail the operation by
+ * returning 0 as the lock mode.
+ */
+uint
+xfs_ilock_data_map_shared_nowait(
+ struct xfs_inode *ip)
+{
+ if (xfs_need_iread_extents(&ip->i_df))
+ return 0;
+ if (!xfs_ilock_nowait(ip, XFS_ILOCK_SHARED))
+ return 0;
+ return XFS_ILOCK_SHARED;
+}
+
+int
+xfs_ilock_data_map_shared_generic(
+ struct xfs_inode *dp,
+ bool nowait)
+{
+ if (nowait)
+ return xfs_ilock_data_map_shared_nowait(dp);
+ return xfs_ilock_data_map_shared(dp);
+}
+
uint
xfs_ilock_attr_map_shared(
struct xfs_inode *ip)
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 7547caf2f2ab..ea206a5a27df 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -490,13 +490,16 @@ int xfs_rename(struct mnt_idmap *idmap,
struct xfs_name *target_name,
struct xfs_inode *target_ip, unsigned int flags);

-void xfs_ilock(xfs_inode_t *, uint);
-int xfs_ilock_nowait(xfs_inode_t *, uint);
-void xfs_iunlock(xfs_inode_t *, uint);
-void xfs_ilock_demote(xfs_inode_t *, uint);
-bool xfs_isilocked(struct xfs_inode *, uint);
-uint xfs_ilock_data_map_shared(struct xfs_inode *);
-uint xfs_ilock_attr_map_shared(struct xfs_inode *);
+void xfs_ilock(struct xfs_inode *ip, uint lockmode);
+int xfs_ilock_nowait(struct xfs_inode *ip, uint lockmode);
+void xfs_iunlock(struct xfs_inode *ip, uint lockmode);
+void xfs_ilock_demote(struct xfs_inode *ip, uint lockmode);
+bool xfs_isilocked(struct xfs_inode *ip, uint lockmode);
+uint xfs_ilock_data_map_shared(struct xfs_inode *ip);
+uint xfs_ilock_data_map_shared_nowait(struct xfs_inode *ip);
+int xfs_ilock_data_map_shared_generic(struct xfs_inode *ip,
+ bool nowait);
+uint xfs_ilock_attr_map_shared(struct xfs_inode *ip);

uint xfs_ip2xflags(struct xfs_inode *);
int xfs_ifree(struct xfs_trans *, struct xfs_inode *);
--
2.25.1