char: Mark /dev/zero and /dev/kmem as not capable of writeback

commit 371d217ee1ff8b418b8f73fb2a34990f951ec2d4 upstream.

These devices don't do any writeback but their device inodes still can get
dirty so mark bdi appropriately so that bdi code does the right thing and files
inodes to lists of bdi carrying the device inodes.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index aef3fb42150e5e75e902ac04d582179aa33b8370..1270f6452e9a8217c5831900d726af090f9a338d 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -822,10 +822,11 @@ static const struct file_operations zero_fops = {
 /*
  * capabilities for /dev/zero
  * - permits private mappings, "copies" are taken of the source of zeros
+ * - no writeback happens
  */
 static struct backing_dev_info zero_bdi = {
        .name           = "char/mem",
-       .capabilities   = BDI_CAP_MAP_COPY,
+       .capabilities   = BDI_CAP_MAP_COPY | BDI_CAP_NO_ACCT_AND_WRITEBACK,
 };
 
 static const struct file_operations full_fops = {

diff --git a/fs/char_dev.c b/fs/char_dev.c
index d6db933df2b27ce43c0fe31d6e35bb0968598891..be7613ebb6618fcb25bd2de01f44ffbac554f6cb 100644 (file)
--- a/fs/char_dev.c
+++ b/fs/char_dev.c
@@ -39,7 +39,9 @@ struct backing_dev_info directly_mappable_cdev_bdi = {
 #endif
                /* permit direct mmap, for read, write or exec */
                BDI_CAP_MAP_DIRECT |
-               BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP),
+               BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP |
+               /* no writeback happens */
+               BDI_CAP_NO_ACCT_AND_WRITEBACK),
 };
 
 static struct kobj_map *cdev_map;