src/patches/suse-2.6.27.25/patches.fixes/blk-set-segment-boundary-mask

   1 Subject: block: fix setting of max_segment_size and seg_boundary mask
   2 From: Milan Broz <mbroz@redhat.com>
   3 Date: Wed Dec 3 12:55:55 2008 +0100:
   4 Git: 0e435ac26e3f951d83338ed3d4ab7dc0fe0055bc
   5
   6 Fix setting of max_segment_size and seg_boundary mask for stacked md/dm
   7 devices.
   8
   9 When stacking devices (LVM over MD over SCSI) some of the request queue
  10 parameters are not set up correctly in some cases by default, namely
  11 max_segment_size and and seg_boundary mask.
  12
  13 If you create MD device over SCSI, these attributes are zeroed.
  14
  15 Problem become when there is over this mapping next device-mapper mapping
  16 - queue attributes are set in DM this way:
  17
  18 request_queue   max_segment_size  seg_boundary_mask
  19 SCSI                65536             0xffffffff
  20 MD RAID1                0                      0
  21 LVM                 65536                 -1 (64bit)
  22
  23 Unfortunately bio_add_page (resp.  bio_phys_segments) calculates number of
  24 physical segments according to these parameters.
  25
  26 During the generic_make_request() is segment cout recalculated and can
  27 increase bio->bi_phys_segments count over the allowed limit.  (After
  28 bio_clone() in stack operation.)
  29
  30 Thi is specially problem in CCISS driver, where it produce OOPS here
  31
  32     BUG_ON(creq->nr_phys_segments > MAXSGENTRIES);
  33
  34 (MAXSEGENTRIES is 31 by default.)
  35
  36 Sometimes even this command is enough to cause oops:
  37
  38   dd iflag=direct if=/dev/<vg>/<lv> of=/dev/null bs=128000 count=10
  39
  40 This command generates bios with 250 sectors, allocated in 32 4k-pages
  41 (last page uses only 1024 bytes).
  42
  43 For LVM layer, it allocates bio with 31 segments (still OK for CCISS),
  44 unfortunatelly on lower layer it is recalculated to 32 segments and this
  45 violates CCISS restriction and triggers BUG_ON().
  46
  47 The patch tries to fix it by:
  48
  49  * initializing attributes above in queue request constructor
  50    blk_queue_make_request()
  51
  52  * make sure that blk_queue_stack_limits() inherits setting
  53
  54  (DM uses its own function to set the limits because it
  55  blk_queue_stack_limits() was introduced later.  It should probably switch
  56  to use generic stack limit function too.)
  57
  58  * sets the default seg_boundary value in one place (blkdev.h)
  59
  60  * use this mask as default in DM (instead of -1, which differs in 64bit)
  61
  62 Bugs related to this:
  63 https://bugzilla.redhat.com/show_bug.cgi?id=471639
  64 http://bugzilla.kernel.org/show_bug.cgi?id=8672
  65
  66 Signed-off-by: Milan Broz <mbroz@redhat.com>
  67 Reviewed-by: Alasdair G Kergon <agk@redhat.com>
  68 Cc: Neil Brown <neilb@suse.de>
  69 Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
  70 Cc: Tejun Heo <htejun@gmail.com>
  71 Cc: Mike Miller <mike.miller@hp.com>
  72 Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
  73 Signed-off-by: Hannes Reinecke <hare@suse.de>
  74
  75 ---
  76  block/blk-core.c       |    2 +-
  77  block/blk-settings.c   |    4 ++++
  78  drivers/md/dm-table.c  |    2 +-
  79  include/linux/blkdev.h |    2 ++
  80  4 files changed, 8 insertions(+), 2 deletions(-)
  81
  82 --- a/block/blk-core.c
  83 +++ b/block/blk-core.c
  84 @@ -596,7 +596,7 @@ blk_init_queue_node(request_fn_proc *rfn
  85                                    1 << QUEUE_FLAG_STACKABLE);
  86         q->queue_lock           = lock;
  87
  88 -       blk_queue_segment_boundary(q, 0xffffffff);
  89 +       blk_queue_segment_boundary(q, BLK_SEG_BOUNDARY_MASK);
  90
  91         blk_queue_make_request(q, __make_request);
  92         blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
  93 --- a/block/blk-settings.c
  94 +++ b/block/blk-settings.c
  95 @@ -125,6 +125,9 @@ void blk_queue_make_request(struct reque
  96         q->nr_requests = BLKDEV_MAX_RQ;
  97         blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
  98         blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
  99 +       blk_queue_segment_boundary(q, BLK_SEG_BOUNDARY_MASK);
 100 +       blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
 101 +
 102         q->make_request_fn = mfn;
 103         q->backing_dev_info.ra_pages =
 104                         (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
 105 @@ -314,6 +317,7 @@ void blk_queue_stack_limits(struct reque
 106         /* zero is "infinity" */
 107         t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
 108         t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
 109 +       t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask, b->seg_boundary_mask);
 110
 111         t->max_phys_segments = min(t->max_phys_segments, b->max_phys_segments);
 112         t->max_hw_segments = min(t->max_hw_segments, b->max_hw_segments);
 113 --- a/drivers/md/dm-table.c
 114 +++ b/drivers/md/dm-table.c
 115 @@ -687,7 +687,7 @@ static void check_for_valid_limits(struc
 116         if (!rs->max_segment_size)
 117                 rs->max_segment_size = MAX_SEGMENT_SIZE;
 118         if (!rs->seg_boundary_mask)
 119 -               rs->seg_boundary_mask = -1;
 120 +               rs->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
 121         if (!rs->bounce_pfn)
 122                 rs->bounce_pfn = -1;
 123  }
 124 --- a/include/linux/blkdev.h
 125 +++ b/include/linux/blkdev.h
 126 @@ -908,6 +908,8 @@ extern void blk_set_cmd_filter_defaults(
 127
 128  #define MAX_SEGMENT_SIZE       65536
 129
 130 +#define BLK_SEG_BOUNDARY_MASK  0xFFFFFFFFUL
 131 +
 132  #define blkdev_entry_to_request(entry) list_entry((entry), struct request, queuelist)
 133
 134  static inline int queue_hardsect_size(struct request_queue *q)