[PATCH 0/3] Fix overflow issues with sysctl values in centiseconds/seconds

[Bart Samwel <bart@samwel.tk>]

Hi Andrew,

Here's a threesome of patches to fix up some issues with the following 
sysctl values:

/proc/sys/vm/laptop_mode
/proc/sys/vm/dirty_writeback_centisecs
/proc/sys/vm/dirty_expire_centisecs

The issues:
1. The values are not range checked when they are set. They all have
a range smaller than the full integer range.
2. Conversion from these centisecond/second values is done on-the-fly 
wherever they are used. This wastes some resources.
3. The conversions are done badly. Conversion from USER_HZ to HZ is done 
by doing "value * USER_HZ / HZ". One day expressed in centiseconds 
already causes an overflow at HZ = 250. This should use 
clock_t_to_jiffies() instead.

The approach:
1. Represent everything in jiffies internally.
2. Do the conversion and range checking in the sysctl interface.

Cheers,
Bart
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