xfs: introduce xfs_rw_lock() helpers for locking the inode
We need to obtain the i_mutex, i_iolock and i_ilock during the read
and write paths. Add a set of wrapper functions to neatly
encapsulate the lock ordering and shared/exclusive semantics to make
the locking easier to follow and get right.
Note that this changes some of the exclusive locking serialisation in
that serialisation will occur against the i_mutex instead of the
XFS_IOLOCK_EXCL. This does not change any behaviour, and it is
arguably more efficient to use the mutex for such serialisation than
the rw_sem.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index c47d7dc0..b5e13fb 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -41,6 +41,40 @@
static const struct vm_operations_struct xfs_file_vm_ops;
/*
+ * Locking primitives for read and write IO paths to ensure we consistently use
+ * and order the inode->i_mutex, ip->i_lock and ip->i_iolock.
+ */
+static inline void
+xfs_rw_ilock(
+ struct xfs_inode *ip,
+ int type)
+{
+ if (type & XFS_IOLOCK_EXCL)
+ mutex_lock(&VFS_I(ip)->i_mutex);
+ xfs_ilock(ip, type);
+}
+
+static inline void
+xfs_rw_iunlock(
+ struct xfs_inode *ip,
+ int type)
+{
+ xfs_iunlock(ip, type);
+ if (type & XFS_IOLOCK_EXCL)
+ mutex_unlock(&VFS_I(ip)->i_mutex);
+}
+
+static inline void
+xfs_rw_ilock_demote(
+ struct xfs_inode *ip,
+ int type)
+{
+ xfs_ilock_demote(ip, type);
+ if (type & XFS_IOLOCK_EXCL)
+ mutex_unlock(&VFS_I(ip)->i_mutex);
+}
+
+/*
* xfs_iozero
*
* xfs_iozero clears the specified range of buffer supplied,
@@ -262,22 +296,21 @@
if (XFS_FORCED_SHUTDOWN(mp))
return -EIO;
- if (unlikely(ioflags & IO_ISDIRECT))
- mutex_lock(&inode->i_mutex);
- xfs_ilock(ip, XFS_IOLOCK_SHARED);
-
if (unlikely(ioflags & IO_ISDIRECT)) {
+ xfs_rw_ilock(ip, XFS_IOLOCK_EXCL);
+
if (inode->i_mapping->nrpages) {
ret = -xfs_flushinval_pages(ip,
(iocb->ki_pos & PAGE_CACHE_MASK),
-1, FI_REMAPF_LOCKED);
+ if (ret) {
+ xfs_rw_iunlock(ip, XFS_IOLOCK_EXCL);
+ return ret;
+ }
}
- mutex_unlock(&inode->i_mutex);
- if (ret) {
- xfs_iunlock(ip, XFS_IOLOCK_SHARED);
- return ret;
- }
- }
+ xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
+ } else
+ xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
trace_xfs_file_read(ip, size, iocb->ki_pos, ioflags);
@@ -285,7 +318,7 @@
if (ret > 0)
XFS_STATS_ADD(xs_read_bytes, ret);
- xfs_iunlock(ip, XFS_IOLOCK_SHARED);
+ xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
return ret;
}
@@ -309,7 +342,7 @@
if (XFS_FORCED_SHUTDOWN(ip->i_mount))
return -EIO;
- xfs_ilock(ip, XFS_IOLOCK_SHARED);
+ xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
trace_xfs_file_splice_read(ip, count, *ppos, ioflags);
@@ -317,7 +350,7 @@
if (ret > 0)
XFS_STATS_ADD(xs_read_bytes, ret);
- xfs_iunlock(ip, XFS_IOLOCK_SHARED);
+ xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
return ret;
}
@@ -338,10 +371,10 @@
*ppos = isize;
if (*ppos > ip->i_size) {
- xfs_ilock(ip, XFS_ILOCK_EXCL);
+ xfs_rw_ilock(ip, XFS_ILOCK_EXCL);
if (*ppos > ip->i_size)
ip->i_size = *ppos;
- xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
}
}
@@ -356,14 +389,22 @@
struct xfs_inode *ip)
{
if (ip->i_new_size) {
- xfs_ilock(ip, XFS_ILOCK_EXCL);
+ xfs_rw_ilock(ip, XFS_ILOCK_EXCL);
ip->i_new_size = 0;
if (ip->i_d.di_size > ip->i_size)
ip->i_d.di_size = ip->i_size;
- xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
}
}
+/*
+ * xfs_file_splice_write() does not use xfs_rw_ilock() because
+ * generic_file_splice_write() takes the i_mutex itself. This, in theory,
+ * couuld cause lock inversions between the aio_write path and the splice path
+ * if someone is doing concurrent splice(2) based writes and write(2) based
+ * writes to the same inode. The only real way to fix this is to re-implement
+ * the generic code here with correct locking orders.
+ */
STATIC ssize_t
xfs_file_splice_write(
struct pipe_inode_info *pipe,
@@ -604,7 +645,6 @@
xfs_fsize_t new_size;
int iolock;
size_t ocount = 0, count;
- int need_i_mutex;
XFS_STATS_INC(xs_write_calls);
@@ -631,21 +671,17 @@
relock:
if (ioflags & IO_ISDIRECT) {
iolock = XFS_IOLOCK_SHARED;
- need_i_mutex = 0;
} else {
iolock = XFS_IOLOCK_EXCL;
- need_i_mutex = 1;
- mutex_lock(&inode->i_mutex);
}
- xfs_ilock(ip, XFS_ILOCK_EXCL|iolock);
-
start:
+ xfs_rw_ilock(ip, XFS_ILOCK_EXCL|iolock);
ret = generic_write_checks(file, &pos, &count,
S_ISBLK(inode->i_mode));
if (ret) {
- xfs_iunlock(ip, XFS_ILOCK_EXCL|iolock);
- goto out_unlock_mutex;
+ xfs_rw_iunlock(ip, XFS_ILOCK_EXCL|iolock);
+ return ret;
}
if (ioflags & IO_ISDIRECT) {
@@ -654,16 +690,20 @@
mp->m_rtdev_targp : mp->m_ddev_targp;
if ((pos & target->bt_smask) || (count & target->bt_smask)) {
- xfs_iunlock(ip, XFS_ILOCK_EXCL|iolock);
+ xfs_rw_iunlock(ip, XFS_ILOCK_EXCL|iolock);
return XFS_ERROR(-EINVAL);
}
- if (!need_i_mutex && (mapping->nrpages || pos > ip->i_size)) {
- xfs_iunlock(ip, XFS_ILOCK_EXCL|iolock);
+ /*
+ * For direct I/O, if there are cached pages or we're extending
+ * the file, we need IOLOCK_EXCL until we're sure the bytes at
+ * the new EOF have been zeroed and/or the cached pages are
+ * flushed out. Upgrade the I/O lock and start again.
+ */
+ if (iolock != XFS_IOLOCK_EXCL &&
+ (mapping->nrpages || pos > ip->i_size)) {
+ xfs_rw_iunlock(ip, XFS_ILOCK_EXCL|iolock);
iolock = XFS_IOLOCK_EXCL;
- need_i_mutex = 1;
- mutex_lock(&inode->i_mutex);
- xfs_ilock(ip, XFS_ILOCK_EXCL|iolock);
goto start;
}
}
@@ -687,11 +727,11 @@
if (pos > ip->i_size) {
ret = -xfs_zero_eof(ip, pos, ip->i_size);
if (ret) {
- xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
goto out_unlock_internal;
}
}
- xfs_iunlock(ip, XFS_ILOCK_EXCL);
+ xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
/*
* If we're writing the file then make sure to clear the
@@ -708,7 +748,7 @@
if ((ioflags & IO_ISDIRECT)) {
if (mapping->nrpages) {
- WARN_ON(need_i_mutex == 0);
+ WARN_ON(iolock != XFS_IOLOCK_EXCL);
ret = -xfs_flushinval_pages(ip,
(pos & PAGE_CACHE_MASK),
-1, FI_REMAPF_LOCKED);
@@ -716,13 +756,10 @@
goto out_unlock_internal;
}
- if (need_i_mutex) {
+ if (iolock == XFS_IOLOCK_EXCL) {
/* demote the lock now the cached pages are gone */
- xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);
- mutex_unlock(&inode->i_mutex);
-
+ xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
iolock = XFS_IOLOCK_SHARED;
- need_i_mutex = 0;
}
trace_xfs_file_direct_write(ip, count, iocb->ki_pos, ioflags);
@@ -740,7 +777,7 @@
count -= ret;
ioflags &= ~IO_ISDIRECT;
- xfs_iunlock(ip, iolock);
+ xfs_rw_iunlock(ip, iolock);
goto relock;
}
} else {
@@ -775,14 +812,9 @@
loff_t end = pos + ret - 1;
int error, error2;
- xfs_iunlock(ip, iolock);
- if (need_i_mutex)
- mutex_unlock(&inode->i_mutex);
-
+ xfs_rw_iunlock(ip, iolock);
error = filemap_write_and_wait_range(mapping, pos, end);
- if (need_i_mutex)
- mutex_lock(&inode->i_mutex);
- xfs_ilock(ip, iolock);
+ xfs_rw_ilock(ip, iolock);
error2 = -xfs_file_fsync(file,
(file->f_flags & __O_SYNC) ? 0 : 1);
@@ -794,10 +826,7 @@
out_unlock_internal:
xfs_aio_write_newsize_update(ip);
- xfs_iunlock(ip, iolock);
- out_unlock_mutex:
- if (need_i_mutex)
- mutex_unlock(&inode->i_mutex);
+ xfs_rw_iunlock(ip, iolock);
return ret;
}