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Date: Mon, 25 Sep 2017 17:14:01 -0600
From: Ross Zwisler <ross.zwisler@...ux.intel.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>,
"Darrick J. Wong" <darrick.wong@...cle.com>,
"J. Bruce Fields" <bfields@...ldses.org>,
Christoph Hellwig <hch@....de>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
Jeff Layton <jlayton@...chiereds.net>,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-nvdimm@...ts.01.org, linux-xfs@...r.kernel.org
Subject: [PATCH 4/7] xfs: protect S_DAX transitions in XFS write path
In the current XFS write I/O path we check IS_DAX() in
xfs_file_write_iter() to decide whether to do DAX I/O, direct I/O or
buffered I/O. This check is done without holding the XFS_IOLOCK, though,
which means that if we allow S_DAX to be manipulated via the inode flag we
can run into this race:
CPU 0 CPU 1
----- -----
xfs_file_write_iter()
IS_DAX() << returns false
xfs_ioctl_setattr()
xfs_ioctl_setattr_dax_invalidate()
xfs_ilock(XFS_MMAPLOCK|XFS_IOLOCK)
sets S_DAX
releases XFS_MMAPLOCK and XFS_IOLOCK
xfs_file_buffered_aio_write()
does buffered I/O to DAX inode, death
Fix this by ensuring that we only check S_DAX when we hold the XFS_IOLOCK
in the write path.
Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
---
fs/xfs/xfs_file.c | 115 +++++++++++++++++++++---------------------------------
1 file changed, 44 insertions(+), 71 deletions(-)
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index ca4c8fd..2816858 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -308,9 +308,7 @@ xfs_zero_eof(
/*
* Common pre-write limit and setup checks.
*
- * Called with the iolocked held either shared and exclusive according to
- * @iolock, and returns with it held. Might upgrade the iolock to exclusive
- * if called for a direct write beyond i_size.
+ * Called with the iolock held in exclusive mode.
*/
STATIC ssize_t
xfs_file_aio_write_checks(
@@ -322,7 +320,6 @@ xfs_file_aio_write_checks(
struct inode *inode = file->f_mapping->host;
struct xfs_inode *ip = XFS_I(inode);
ssize_t error = 0;
- size_t count = iov_iter_count(from);
bool drained_dio = false;
restart:
@@ -335,21 +332,9 @@ xfs_file_aio_write_checks(
return error;
/*
- * For changing security info in file_remove_privs() we need i_rwsem
- * exclusively.
- */
- if (*iolock == XFS_IOLOCK_SHARED && !IS_NOSEC(inode)) {
- xfs_iunlock(ip, *iolock);
- *iolock = XFS_IOLOCK_EXCL;
- xfs_ilock(ip, *iolock);
- goto restart;
- }
- /*
* If the offset is beyond the size of the file, we need to zero any
* blocks that fall between the existing EOF and the start of this
- * write. If zeroing is needed and we are currently holding the
- * iolock shared, we need to update it to exclusive which implies
- * having to redo all checks before.
+ * write.
*
* We need to serialise against EOF updates that occur in IO
* completions here. We want to make sure that nobody is changing the
@@ -365,12 +350,6 @@ xfs_file_aio_write_checks(
spin_unlock(&ip->i_flags_lock);
if (!drained_dio) {
- if (*iolock == XFS_IOLOCK_SHARED) {
- xfs_iunlock(ip, *iolock);
- *iolock = XFS_IOLOCK_EXCL;
- xfs_ilock(ip, *iolock);
- iov_iter_reexpand(from, count);
- }
/*
* We now have an IO submission barrier in place, but
* AIO can do EOF updates during IO completion and hence
@@ -491,7 +470,8 @@ xfs_dio_write_end_io(
STATIC ssize_t
xfs_file_dio_aio_write(
struct kiocb *iocb,
- struct iov_iter *from)
+ struct iov_iter *from,
+ int *iolock)
{
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
@@ -500,7 +480,6 @@ xfs_file_dio_aio_write(
struct xfs_mount *mp = ip->i_mount;
ssize_t ret = 0;
int unaligned_io = 0;
- int iolock;
size_t count = iov_iter_count(from);
struct xfs_buftarg *target = XFS_IS_REALTIME_INODE(ip) ?
mp->m_rtdev_targp : mp->m_ddev_targp;
@@ -510,11 +489,12 @@ xfs_file_dio_aio_write(
return -EINVAL;
/*
- * Don't take the exclusive iolock here unless the I/O is unaligned to
- * the file system block size. We don't need to consider the EOF
- * extension case here because xfs_file_aio_write_checks() will relock
- * the inode as necessary for EOF zeroing cases and fill out the new
- * inode size as appropriate.
+ * We hold the exclusive iolock via our caller. After the common
+ * write checks we will demote it to a shared iolock unless the I/O is
+ * unaligned to the file system block size. We don't need to consider
+ * the EOF extension case here because xfs_file_aio_write_checks()
+ * will deal with EOF zeroing cases and fill out the new inode size as
+ * appropriate.
*/
if ((iocb->ki_pos & mp->m_blockmask) ||
((iocb->ki_pos + count) & mp->m_blockmask)) {
@@ -528,26 +508,17 @@ xfs_file_dio_aio_write(
trace_xfs_reflink_bounce_dio_write(ip, iocb->ki_pos, count);
return -EREMCHG;
}
- iolock = XFS_IOLOCK_EXCL;
- } else {
- iolock = XFS_IOLOCK_SHARED;
}
- if (!xfs_ilock_nowait(ip, iolock)) {
- if (iocb->ki_flags & IOCB_NOWAIT)
- return -EAGAIN;
- xfs_ilock(ip, iolock);
- }
- ret = xfs_file_aio_write_checks(iocb, from, &iolock);
+ ret = xfs_file_aio_write_checks(iocb, from, iolock);
if (ret)
goto out;
count = iov_iter_count(from);
/*
* If we are doing unaligned IO, wait for all other IO to drain,
- * otherwise demote the lock if we had to take the exclusive lock
- * for other reasons in xfs_file_aio_write_checks.
+ * otherwise demote the lock.
*/
if (unaligned_io) {
/* If we are going to wait for other DIO to finish, bail */
@@ -557,15 +528,14 @@ xfs_file_dio_aio_write(
} else {
inode_dio_wait(inode);
}
- } else if (iolock == XFS_IOLOCK_EXCL) {
+ } else if (*iolock == XFS_IOLOCK_EXCL) {
xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);
- iolock = XFS_IOLOCK_SHARED;
+ *iolock = XFS_IOLOCK_SHARED;
}
trace_xfs_file_direct_write(ip, count, iocb->ki_pos);
ret = iomap_dio_rw(iocb, from, &xfs_iomap_ops, xfs_dio_write_end_io);
out:
- xfs_iunlock(ip, iolock);
/*
* No fallback to buffered IO on errors for XFS, direct IO will either
@@ -578,22 +548,16 @@ xfs_file_dio_aio_write(
static noinline ssize_t
xfs_file_dax_write(
struct kiocb *iocb,
- struct iov_iter *from)
+ struct iov_iter *from,
+ int *iolock)
{
struct inode *inode = iocb->ki_filp->f_mapping->host;
struct xfs_inode *ip = XFS_I(inode);
- int iolock = XFS_IOLOCK_EXCL;
ssize_t ret, error = 0;
size_t count;
loff_t pos;
- if (!xfs_ilock_nowait(ip, iolock)) {
- if (iocb->ki_flags & IOCB_NOWAIT)
- return -EAGAIN;
- xfs_ilock(ip, iolock);
- }
-
- ret = xfs_file_aio_write_checks(iocb, from, &iolock);
+ ret = xfs_file_aio_write_checks(iocb, from, iolock);
if (ret)
goto out;
@@ -607,14 +571,14 @@ xfs_file_dax_write(
error = xfs_setfilesize(ip, pos, ret);
}
out:
- xfs_iunlock(ip, iolock);
return error ? error : ret;
}
STATIC ssize_t
xfs_file_buffered_aio_write(
struct kiocb *iocb,
- struct iov_iter *from)
+ struct iov_iter *from,
+ int *iolock)
{
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
@@ -622,16 +586,12 @@ xfs_file_buffered_aio_write(
struct xfs_inode *ip = XFS_I(inode);
ssize_t ret;
int enospc = 0;
- int iolock;
if (iocb->ki_flags & IOCB_NOWAIT)
return -EOPNOTSUPP;
write_retry:
- iolock = XFS_IOLOCK_EXCL;
- xfs_ilock(ip, iolock);
-
- ret = xfs_file_aio_write_checks(iocb, from, &iolock);
+ ret = xfs_file_aio_write_checks(iocb, from, iolock);
if (ret)
goto out;
@@ -653,32 +613,35 @@ xfs_file_buffered_aio_write(
* running at the same time.
*/
if (ret == -EDQUOT && !enospc) {
- xfs_iunlock(ip, iolock);
+ xfs_iunlock(ip, *iolock);
enospc = xfs_inode_free_quota_eofblocks(ip);
if (enospc)
- goto write_retry;
+ goto lock_retry;
enospc = xfs_inode_free_quota_cowblocks(ip);
if (enospc)
- goto write_retry;
- iolock = 0;
+ goto lock_retry;
+ *iolock = 0;
} else if (ret == -ENOSPC && !enospc) {
struct xfs_eofblocks eofb = {0};
enospc = 1;
xfs_flush_inodes(ip->i_mount);
- xfs_iunlock(ip, iolock);
+ xfs_iunlock(ip, *iolock);
eofb.eof_flags = XFS_EOF_FLAGS_SYNC;
xfs_icache_free_eofblocks(ip->i_mount, &eofb);
xfs_icache_free_cowblocks(ip->i_mount, &eofb);
- goto write_retry;
+ goto lock_retry;
}
current->backing_dev_info = NULL;
out:
- if (iolock)
- xfs_iunlock(ip, iolock);
return ret;
+lock_retry:
+ xfs_ilock(ip, *iolock);
+ if (IS_DAX(inode))
+ return -EAGAIN;
+ goto write_retry;
}
STATIC ssize_t
@@ -692,6 +655,7 @@ xfs_file_write_iter(
struct xfs_inode *ip = XFS_I(inode);
ssize_t ret;
size_t ocount = iov_iter_count(from);
+ int iolock = XFS_IOLOCK_EXCL;
XFS_STATS_INC(ip->i_mount, xs_write_calls);
@@ -701,8 +665,14 @@ xfs_file_write_iter(
if (XFS_FORCED_SHUTDOWN(ip->i_mount))
return -EIO;
+ if (!xfs_ilock_nowait(ip, iolock)) {
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ return -EAGAIN;
+ xfs_ilock(ip, iolock);
+ }
+
if (IS_DAX(inode))
- ret = xfs_file_dax_write(iocb, from);
+ ret = xfs_file_dax_write(iocb, from, &iolock);
else if (iocb->ki_flags & IOCB_DIRECT) {
/*
* Allow a directio write to fall back to a buffered
@@ -710,14 +680,17 @@ xfs_file_write_iter(
* CoW. In all other directio scenarios we do not
* allow an operation to fall back to buffered mode.
*/
- ret = xfs_file_dio_aio_write(iocb, from);
+ ret = xfs_file_dio_aio_write(iocb, from, &iolock);
if (ret == -EREMCHG)
goto buffered;
} else {
buffered:
- ret = xfs_file_buffered_aio_write(iocb, from);
+ ret = xfs_file_buffered_aio_write(iocb, from, &iolock);
}
+ if (iolock)
+ xfs_iunlock(ip, iolock);
+
if (ret > 0) {
XFS_STATS_ADD(ip->i_mount, xs_write_bytes, ret);
--
2.9.5
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