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



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