Remove the bio_empty_barrier() check.

To determine whether the kernel is capable of handling empty barrier
BIOs, we check for the presence of the bio_empty_barrier() macro,
which was introduced in 2.6.24. If this macro is defined, then we can
flush disk vdevs; if it isn't, then flushing is disabled.

Unfortunately, the bio_empty_barrier() macro was removed in 2.6.37,
even though the kernel is still capable of handling empty barrier BIOs.

As a result, flushing is effectively disabled on kernels >= 2.6.37,
meaning that starting from this kernel version, zfs doesn't use
barriers to guarantee on-disk data consistency. This is quite bad and
can lead to potential data corruption on power failures.

This patch fixes the issue by removing the configure check for
bio_empty_barrier(), as we don't support kernels <= 2.6.24 anymore.

Thanks to Richard Kojedzinszky for catching this nasty bug.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1318

diff --git a/config/kernel-bio-empty-barrier.m4 b/config/kernel-bio-empty-barrier.m4
deleted file mode 100644 (file)
index fda16b3..0000000
--- a/config/kernel-bio-empty-barrier.m4
+++ /dev/null
@@ -1,19 +0,0 @@
-dnl #
-dnl # 2.6.24 API change
-dnl # Empty write barriers are now supported and we should use them.
-dnl #
-AC_DEFUN([ZFS_AC_KERNEL_BIO_EMPTY_BARRIER], [
-       AC_MSG_CHECKING([whether bio_empty_barrier() is defined])
-       ZFS_LINUX_TRY_COMPILE([
-               #include <linux/bio.h>
-       ],[
-               struct bio bio;
-               (void)bio_empty_barrier(&bio);
-       ],[
-               AC_MSG_RESULT(yes)
-               AC_DEFINE(HAVE_BIO_EMPTY_BARRIER, 1,
-                         [bio_empy_barrier() is defined])
-       ],[
-               AC_MSG_RESULT(no)
-       ])
-])

diff --git a/config/kernel.m4 b/config/kernel.m4
index 5623785..9d5aa46 100644 (file)
--- a/config/kernel.m4
+++ b/config/kernel.m4
@@ -16,7 +16,6 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
        ZFS_AC_KERNEL_INVALIDATE_BDEV_ARGS
        ZFS_AC_KERNEL_BDEV_LOGICAL_BLOCK_SIZE
        ZFS_AC_KERNEL_BDEV_PHYSICAL_BLOCK_SIZE
-       ZFS_AC_KERNEL_BIO_EMPTY_BARRIER
        ZFS_AC_KERNEL_BIO_FAILFAST
        ZFS_AC_KERNEL_BIO_FAILFAST_DTD
        ZFS_AC_KERNEL_REQ_FAILFAST_MASK

diff --git a/module/zfs/vdev_disk.c b/module/zfs/vdev_disk.c
index cbf0a4d..e902a70 100644 (file)
--- a/module/zfs/vdev_disk.c
+++ b/module/zfs/vdev_disk.c
@@ -604,8 +604,6 @@ vdev_disk_physio(struct block_device *bdev, caddr_t kbuf,
        return __vdev_disk_physio(bdev, NULL, kbuf, size, offset, flags);
 }
 
-/* 2.6.24 API change */
-#ifdef HAVE_BIO_EMPTY_BARRIER
 BIO_END_IO_PROTO(vdev_disk_io_flush_completion, bio, size, rc)
 {
        zio_t *zio = bio->bi_private;
@@ -646,13 +644,6 @@ vdev_disk_io_flush(struct block_device *bdev, zio_t *zio)
 
        return 0;
 }
-#else
-static int
-vdev_disk_io_flush(struct block_device *bdev, zio_t *zio)
-{
-       return ENOTSUP;
-}
-#endif /* HAVE_BIO_EMPTY_BARRIER */
 
 static int
 vdev_disk_io_start(zio_t *zio)