July 20, 2001

Linux 2.4.7-pre9

Author: JT Smith

Linus Torvalds has a few words on 2.4.7-pre9, reprinted from the kernel list. kernel.org and the usual mirrors should have it by now; read on for the message from Torvalds.
                  I'm getting ready to do a 2.4.7, but one of the fixes in 2.4.7 is a nasty
                  SMP race that was found and made it clear that using an old trick of
                  having a semaphore on the stack and doing "down()" on it to wait for some
                  event (that would do the "up()") was a really bad idea.

                  This kind of trick was used in the kernel vfork() implementation, and also
                  in block device "wait for request completion". I've fixed both with a new
                  and fairly simple "wait for completion" infrastructure, but I'd like
                  especially SCSI device driver writers to check their own drivers as a
                  result before I make the final 2.4.7.

                  I've changed all generic code, so drivers are all expected to compile and
                  work. However, some SCSI drivers use the semaphore trick in their own
                  code, and I've not mucked with that. It's not worth worrying about too
                  much, as the race is basically impossible to hit (famous last words), but
                  I wanted a heads-up and people to give it a quick look. I also wanted to
                  have people who actually have the hardware in question to verify that my
                  untested (but on the face of it obvious) changes are indeed working.

                  So please give it a quick spin,

                                  Linus

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