[PATCH] vfs: partially revert "don't allow writes to swap files"

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

In commit dc617f29dbe5 we tried to prevent userspace programs from
writing to active swap devices.  However, it turns out that userspace
hibernation requires the ability to write the hibernation image to a
swap device, so revert the write path checks.

Fixes: dc617f29dbe5 ("vfs: don't allow writes to swap files")
Reported-by: Domenico Andreoli <domenico.andreoli@linux.com>
Reported-by: Marian Klein <mkleinsoft@gmail.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/block_dev.c |    3 ---
 mm/filemap.c   |    3 ---
 mm/memory.c    |    4 ----
 mm/mmap.c      |    8 ++------
 4 files changed, 2 insertions(+), 16 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 69bf2fb6f7cd..08b088dac1f0 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -2001,9 +2001,6 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (bdev_read_only(I_BDEV(bd_inode)))
 		return -EPERM;
 
-	if (IS_SWAPFILE(bd_inode))
-		return -ETXTBSY;
-
 	if (!iov_iter_count(from))
 		return 0;
 
diff --git a/mm/filemap.c b/mm/filemap.c
index 1784478270e1..d1b8cd15b2bf 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2920,9 +2920,6 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
 	loff_t count;
 	int ret;
 
-	if (IS_SWAPFILE(inode))
-		return -ETXTBSY;
-
 	if (!iov_iter_count(from))
 		return 0;
 
diff --git a/mm/memory.c b/mm/memory.c
index 0bccc622e482..e908490f7034 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2357,10 +2357,6 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
 
 	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
 
-	if (vmf->vma->vm_file &&
-	    IS_SWAPFILE(vmf->vma->vm_file->f_mapping->host))
-		return VM_FAULT_SIGBUS;
-
 	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
 	/* Restore original flags so that caller is not surprised */
 	vmf->flags = old_flags;
diff --git a/mm/mmap.c b/mm/mmap.c
index d681a20eb4ea..77d086139e13 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1461,12 +1461,8 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 		case MAP_SHARED_VALIDATE:
 			if (flags & ~flags_mask)
 				return -EOPNOTSUPP;
-			if (prot & PROT_WRITE) {
-				if (!(file->f_mode & FMODE_WRITE))
-					return -EACCES;
-				if (IS_SWAPFILE(file->f_mapping->host))
-					return -ETXTBSY;
-			}
+			if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
+				return -EACCES;
 
 			/*
 			 * Make sure we don't allow writing to an append-only