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-rw-r--r--fs/ext4/file.c60
1 files changed, 59 insertions, 1 deletions
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 2e8322c..7b80d54 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -55,11 +55,47 @@ static int ext4_release_file(struct inode *inode, struct file *filp)
return 0;
}
+static void ext4_aiodio_wait(struct inode *inode)
+{
+ wait_queue_head_t *wq = ext4_ioend_wq(inode);
+
+ wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_aiodio_unwritten) == 0));
+}
+
+/*
+ * This tests whether the IO in question is block-aligned or not.
+ * Ext4 utilizes unwritten extents when hole-filling during direct IO, and they
+ * are converted to written only after the IO is complete. Until they are
+ * mapped, these blocks appear as holes, so dio_zero_block() will assume that
+ * it needs to zero out portions of the start and/or end block. If 2 AIO
+ * threads are at work on the same unwritten block, they must be synchronized
+ * or one thread will zero the other's data, causing corruption.
+ */
+static int
+ext4_unaligned_aio(struct inode *inode, const struct iovec *iov,
+ unsigned long nr_segs, loff_t pos)
+{
+ struct super_block *sb = inode->i_sb;
+ int blockmask = sb->s_blocksize - 1;
+ size_t count = iov_length(iov, nr_segs);
+ loff_t final_size = pos + count;
+
+ if (pos >= inode->i_size)
+ return 0;
+
+ if ((pos & blockmask) || (final_size & blockmask))
+ return 1;
+
+ return 0;
+}
+
static ssize_t
ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t pos)
{
struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
+ int unaligned_aio = 0;
+ int ret;
/*
* If we have encountered a bitmap-format file, the size limit
@@ -78,9 +114,31 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
nr_segs = iov_shorten((struct iovec *)iov, nr_segs,
sbi->s_bitmap_maxbytes - pos);
}
+ } else if (unlikely((iocb->ki_filp->f_flags & O_DIRECT) &&
+ !is_sync_kiocb(iocb))) {
+ unaligned_aio = ext4_unaligned_aio(inode, iov, nr_segs, pos);
}
- return generic_file_aio_write(iocb, iov, nr_segs, pos);
+ /* Unaligned direct AIO must be serialized; see comment above */
+ if (unaligned_aio) {
+ static unsigned long unaligned_warn_time;
+
+ /* Warn about this once per day */
+ if (printk_timed_ratelimit(&unaligned_warn_time, 60*60*24*HZ))
+ ext4_msg(inode->i_sb, KERN_WARNING,
+ "Unaligned AIO/DIO on inode %ld by %s; "
+ "performance will be poor.",
+ inode->i_ino, current->comm);
+ mutex_lock(ext4_aio_mutex(inode));
+ ext4_aiodio_wait(inode);
+ }
+
+ ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
+
+ if (unaligned_aio)
+ mutex_unlock(ext4_aio_mutex(inode));
+
+ return ret;
}
static const struct vm_operations_struct ext4_file_vm_ops = {
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