On Tue, 2011-05-17 at 23:27 +0200, Ingo Molnar wrote:* John Stultz<john.stultz@xxxxxxxxxx> wrote:
The implicit rules for current->comm access being safe without locking are no
longer true. Accessing current->comm without holding the task lock may result
in null or incomplete strings (however, access won't run off the end of the
string).
This is rather unfortunate - task->comm is used in a number of performance
critical codepaths such as tracing.
Why does this matter so much? A NULL string is not a big deal.
Note, since task->comm is 16 bytes there's the CMPXCHG16B instruction on x86
which could be used to update it atomically, should atomicity really be
desired.
The changelog also fails to mention _WHY_ this is no longer true. Nor
does it treat why making it true again isn't an option.
Who is changing another task's comm? That's just silly.