block: hold ->invalidate_lock in blkdev_fallocate

When running ->fallocate(), blkdev_fallocate() should hold
mapping->invalidate_lock to prevent page cache from being accessed,
otherwise stale data may be read in page cache.

Without this patch, blktests block/009 fails sometimes. With this patch,
block/009 can pass always.

Also as Jan pointed out, no pages can be created in the discarded area
while you are holding the invalidate_lock, so remove the 2nd
truncate_bdev_range().

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210923023751.1441091-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/fops.c b/block/fops.c
index ffce6f6..1e970c2 100644 (file)
--- a/block/fops.c
+++ b/block/fops.c
@@ -14,6 +14,7 @@
 #include <linux/task_io_accounting_ops.h>
 #include <linux/falloc.h>
 #include <linux/suspend.h>
+#include <linux/fs.h>
 #include "blk.h"
 
 static struct inode *bdev_file_inode(struct file *file)
@@ -553,7 +554,8 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 static long blkdev_fallocate(struct file *file, int mode, loff_t start,
                             loff_t len)
 {
-       struct block_device *bdev = I_BDEV(bdev_file_inode(file));
+       struct inode *inode = bdev_file_inode(file);
+       struct block_device *bdev = I_BDEV(inode);
        loff_t end = start + len - 1;
        loff_t isize;
        int error;
@@ -580,10 +582,12 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
        if ((start | len) & (bdev_logical_block_size(bdev) - 1))
                return -EINVAL;
 
+       filemap_invalidate_lock(inode->i_mapping);
+
        /* Invalidate the page cache, including dirty pages. */
        error = truncate_bdev_range(bdev, file->f_mode, start, end);
        if (error)
-               return error;
+               goto fail;
 
        switch (mode) {
        case FALLOC_FL_ZERO_RANGE:
@@ -600,17 +604,12 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
                                             GFP_KERNEL, 0);
                break;
        default:
-               return -EOPNOTSUPP;
+               error = -EOPNOTSUPP;
        }
-       if (error)
-               return error;
 
-       /*
-        * Invalidate the page cache again; if someone wandered in and dirtied
-        * a page, we just discard it - userspace has no way of knowing whether
-        * the write happened before or after discard completing...
-        */
-       return truncate_bdev_range(bdev, file->f_mode, start, end);
+ fail:
+       filemap_invalidate_unlock(inode->i_mapping);
+       return error;
 }
 
 const struct file_operations def_blk_fops = {