diff options
| -rw-r--r-- | fs/xfs/xfs_file.c | 42 |
1 files changed, 31 insertions, 11 deletions
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 396ef36dcd0a..c068dcd414f4 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -384,21 +384,30 @@ restart: } 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. 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. + * + * We need to serialise against EOF updates that occur in IO completions + * here. We want to make sure that nobody is changing the size while we + * do this check until we have placed an IO barrier (i.e. hold the + * XFS_IOLOCK_EXCL) that prevents new IO from being dispatched. The + * spinlock effectively forms a memory barrier once we have the + * XFS_IOLOCK_EXCL so we are guaranteed to see the latest EOF value and + * hence be able to correctly determine if we need to run zeroing. * - * We need to serialise against EOF updates that occur in IO - * completions here. We want to make sure that nobody is changing the - * size while we do this check until we have placed an IO barrier (i.e. - * hold the XFS_IOLOCK_EXCL) that prevents new IO from being dispatched. - * The spinlock effectively forms a memory barrier once we have the - * XFS_IOLOCK_EXCL so we are guaranteed to see the latest EOF value - * and hence be able to correctly determine if we need to run zeroing. + * We can do an unlocked check here safely as IO completion can only + * extend EOF. Truncate is locked out at this point, so the EOF can + * not move backwards, only forwards. Hence we only need to take the + * slow path and spin locks when we are at or beyond the current EOF. */ + if (iocb->ki_pos <= i_size_read(inode)) + goto out; + spin_lock(&ip->i_flags_lock); isize = i_size_read(inode); if (iocb->ki_pos > isize) { @@ -426,7 +435,7 @@ restart: drained_dio = true; goto restart; } - + trace_xfs_zero_eof(ip, isize, iocb->ki_pos - isize); error = iomap_zero_range(inode, isize, iocb->ki_pos - isize, NULL, &xfs_buffered_write_iomap_ops); @@ -435,6 +444,7 @@ restart: } else spin_unlock(&ip->i_flags_lock); +out: return file_modified(file); } @@ -500,7 +510,17 @@ xfs_dio_write_end_io( * other IO completions here to update the EOF. Failing to serialise * here can result in EOF moving backwards and Bad Things Happen when * that occurs. + * + * As IO completion only ever extends EOF, we can do an unlocked check + * here to avoid taking the spinlock. If we land within the current EOF, + * then we do not need to do an extending update at all, and we don't + * need to take the lock to check this. If we race with an update moving + * EOF, then we'll either still be beyond EOF and need to take the lock, + * or we'll be within EOF and we don't need to take it at all. */ + if (offset + size <= i_size_read(inode)) + goto out; + spin_lock(&ip->i_flags_lock); if (offset + size > i_size_read(inode)) { i_size_write(inode, offset + size); |