Re: [PATCH v9 06/10] iomap: fix iomap_dio_zero() for fs bs > system page size

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On 7/4/24 13:23, Pankaj Raghav (Samsung) wrote:
From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>

iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
< fs block size. iomap_dio_zero() has an implicit assumption that fs block
size < page_size. This is true for most filesystems at the moment.

If the block size > page size, this will send the contents of the page
next to zero page(as len > PAGE_SIZE) to the underlying block device,
causing FS corruption.

iomap is a generic infrastructure and it should not make any assumptions
about the fs block size and the page size of the system.

Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
  fs/iomap/buffered-io.c |  4 ++--
  fs/iomap/direct-io.c   | 45 ++++++++++++++++++++++++++++++++++++------
  2 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index f420c53d86acc..d745f718bcde8 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -2007,10 +2007,10 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
  }
  EXPORT_SYMBOL_GPL(iomap_writepages);
-static int __init iomap_init(void)
+static int __init iomap_buffered_init(void)
  {
  	return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
  			   offsetof(struct iomap_ioend, io_bio),
  			   BIOSET_NEED_BVECS);
  }
-fs_initcall(iomap_init);
+fs_initcall(iomap_buffered_init);
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index f3b43d223a46e..c02b266bba525 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -11,6 +11,7 @@
  #include <linux/iomap.h>
  #include <linux/backing-dev.h>
  #include <linux/uio.h>
+#include <linux/set_memory.h>
  #include <linux/task_io_accounting_ops.h>
  #include "trace.h"
@@ -27,6 +28,13 @@
  #define IOMAP_DIO_WRITE		(1U << 30)
  #define IOMAP_DIO_DIRTY		(1U << 31)
+/*
+ * Used for sub block zeroing in iomap_dio_zero()
+ */
+#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
+#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
+static struct page *zero_page;
+

There are other users of ZERO_PAGE, most notably in fs/direct-io.c and block/blk-lib.c. Any chance to make this available to them?

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich





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