[PATCH 0/4] Set max_discard_sectors maximal value to UINT_MAX>>9

[Gwendal Grignou]

Without this change, 'blkdiscard /dev/mmcblk0' would panic:
Because max_discard_sectors was set to 4G sectors, discard request issued
on behalf of blkdiscard would be merged, leading to request larger than 4GB:
[  169.035929] __end_that: dev mmcblk0: type=1, flags=122c8081
[  169.041464]   sector 0, nr/cnr 0/4294966272
[  169.045689]   bio ebb7a380, biotail ebb7aa80, buffer   (null), len 0
[  169.052106] blk_update_request: bio idx 0 >= vcnt 0
[  169.057068] request botched: dev mmcblk0: type=1, flags=122c8081
[  169.063138]   sector 0, nr/cnr 0/4294966272
[  169.067436]   bio ebb7a380, biotail ebb7aa80, buffer   (null), len 0
The IOCTL would be stuck in the kernel, a watchdog would reboot the machine.

After this change, blkdiscard works fine. With blktrace/blkparse, I verified
the discard requests are sane: 8387584 is 4GB in sectors rounded down.
Example of a ~16GB device:
 9368  Q   D 0 + 8387584 [blkdiscard]
    0  m   N cfq9368 alloced
 9368  G   D 0 + 8387584 [blkdiscard]
 9368  P   N [blkdiscard]
 9368  Q   D 8387584 + 8387584 [blkdiscard]
 9368  G   D 8387584 + 8387584 [blkdiscard]
 9368  Q   D 16775168 + 8387584 [blkdiscard]
 9368  G   D 16775168 + 8387584 [blkdiscard]
 9368  Q   D 25162752 + 5372928 [blkdiscard]
 9368  G   D 25162752 + 5372928 [blkdiscard]
 9368  I   D 0 + 8387584 [blkdiscard]
    0  m   N cfq9368 insert_request
    0  m   N cfq9368 add_to_rr
 9368  I   D 8387584 + 8387584 [blkdiscard]
    0  m   N cfq9368 insert_request
 9368  I   D 16775168 + 8387584 [blkdiscard]
    0  m   N cfq9368 insert_request
 9368  I   D 25162752 + 5372928 [blkdiscard]
    0  m   N cfq9368 insert_request
 9368  U   N [blkdiscard] 4
 ...

I fixed the other locations where max_discard_sectors was set to
UINT_MAX and checked the other settings were in units of 512 bytes
sectors.

Gwendal Grignou (4):
  Limit max_discard_sectors to UINT_MAX>>9
  Limit max_discard_sectors to UINT_MAX>>9
  Limit max_discard_sectors to UINT_MAX>>9
  Limit max_discard_sectors to UINT_MAX>>9

 block/blk-lib.c           | 2 +-
 drivers/block/nbd.c       | 2 +-
 drivers/mmc/core/core.c   | 6 ++++--
 drivers/mtd/mtd_blkdevs.c | 2 +-
 4 files changed, 7 insertions(+), 5 deletions(-)

-- 
1.9.1.423.g4596e3a