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  1. 05 8月, 2009 2 次提交
    • L
      tty-ldisc: turn ldisc user count into a proper refcount · 65b77046
      由 Linus Torvalds 提交于 
      By using the user count for the actual lifetime rules, we can get rid of
the silly "wait_for_idle" logic, because any busy ldisc will
automatically stay around until the last user releases it.  This avoids
a host of odd issues, and simplifies the code.

So now, when the last ldisc reference is dropped, we just release the
ldisc operations struct reference, and free the ldisc.

It looks obvious enough, and it does work for me, but the counting
_could_ be off. It probably isn't (bad counting in the new version would
generally imply that the old code did something really bad, like free an
ldisc with a non-zero count), but it does need some testing, and
preferably somebody looking at it.

With this change, both 'tty_ldisc_put()' and 'tty_ldisc_deref()' are
just aliases for the new ref-counting 'put_ldisc()'. Both of them
decrement the ldisc user count and free it if it goes down to zero.
They're identical functions, in other words.

But the reason they still exist as sepate functions is that one of them
was exported (tty_ldisc_deref) and had a stupid name (so I don't want to
use it as the main name), and the other one was used in multiple places
(and I didn't want to make the patch larger just to rename the users).

In addition to the refcounting, I did do some minimal cleanup. For
example, now "tty_ldisc_try()" actually returns the ldisc it got under
the lock, rather than returning true/false and then the caller would
look up the ldisc again (now without the protection of the lock).

That said, there's tons of dubious use of 'tty->ldisc' without obviously
proper locking or refcounting left. I expressly did _not_ want to try to
fix it all, keeping the patch minimal. There may or may not be bugs in
that kind of code, but they wouldn't be _new_ bugs.

That said, even if the bugs aren't new, the timing and lifetime will
change. For example, some silly code may depend on the 'tty->ldisc'
pointer not changing because they hold a refcount on the 'ldisc'. And
that's no longer true - if you hold a ref on the ldisc, the 'ldisc'
itself is safe, but tty->ldisc may change.

So the proper locking (remains) to hold tty->ldisc_mutex if you expect
tty->ldisc to be stable. That's not really a _new_ rule, but it's an
example of something that the old code might have unintentionally
depended on and hidden bugs.

Whatever. The patch _looks_ sensible to me. The only users of
ldisc->users are:
 - get_ldisc() - atomically increment the count

 - put_ldisc() - atomically decrements the count and releases if zero

 - tty_ldisc_try_get() - creates the ldisc, and sets the count to 1.
   The ldisc should then either be released, or be attached to a tty.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Tested-by: NOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Tested-by: NSergey Senozhatsky <sergey.senozhatsky@mail.by>
Acked-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
      65b77046
    • L
      tty-ldisc: make refcount be atomic_t 'users' count · 18eac1cc
      由 Linus Torvalds 提交于 
      This is pure preparation of changing the ldisc reference counting to be
a true refcount that defines the lifetime of the ldisc.  But this is a
purely syntactic change for now to make the next steps easier.

This patch should make no semantic changes at all. But I wanted to make
the ldisc refcount be an atomic (I will be touching it without locks
soon enough), and I wanted to rename it so that there isn't quite as
much confusion between 'ldo->refcount' (ldisk operations refcount) and
'ld->refcount' (ldisc refcount itself) in the same file.

So it's now an atomic 'ld->users' count. It still starts at zero,
despite having a reference from 'tty->ldisc', but that will change once
we turn it into a _real_ refcount.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Tested-by: NOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Tested-by: NSergey Senozhatsky <sergey.senozhatsky@mail.by>
Acked-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
      18eac1cc
  3. 03 8月, 2009 21 次提交
  5. 02 8月, 2009 10 次提交
  7. 01 8月, 2009 6 次提交
  9. 31 7月, 2009 1 次提交