From 5f2edd80fc90f7699d3f3274153b723af5f0e152 Mon Sep 17 00:00:00 2001 From: ed Date: Wed, 11 Feb 2009 16:28:49 +0000 Subject: Serialize write() calls on TTYs. Just like the old TTY layer, the current MPSAFE TTY layer does not make any attempt to serialize calls of write(). Data is copied into the kernel in 256 (TTY_STACKBUF) byte chunks. If a write() call occurs at the same time, the data may interleave. This is especially likely when the TTY starts blocking, because the output queue reaches the high watermark. I've implemented this by adding a new flag, TTY_BUSY_OUT, which is used to mark a TTY as having a thread stuck in write(). Because I don't want non-blocking processes to be possibly blocked by a sleeping thread, I'm still allowing it to bypass the protection. According to this message, the Linux kernel returns EAGAIN in such cases, but I think that's a little too restrictive: http://kerneltrap.org/index.php?q=mailarchive/linux-kernel/2007/5/2/85418/thread PR: kern/118287 --- usr.sbin/pstat/pstat.8 | 5 +++++ usr.sbin/pstat/pstat.c | 5 +++++ 2 files changed, 10 insertions(+) (limited to 'usr.sbin/pstat') diff --git a/usr.sbin/pstat/pstat.8 b/usr.sbin/pstat/pstat.8 index b92abd8..5e3760c 100644 --- a/usr.sbin/pstat/pstat.8 +++ b/usr.sbin/pstat/pstat.8 @@ -206,6 +206,11 @@ block mode input routine in use connection lost .It s i/o being snooped +.It b +busy in +.Xr read 2 +or +.Xr write 2 .El .Pp The diff --git a/usr.sbin/pstat/pstat.c b/usr.sbin/pstat/pstat.c index 2cb52fe..8272eee 100644 --- a/usr.sbin/pstat/pstat.c +++ b/usr.sbin/pstat/pstat.c @@ -315,6 +315,11 @@ static struct { { TF_ZOMBIE, 'Z' }, { TF_HOOK, 's' }, + /* Keep these together -> 'bi' and 'bo'. */ + { TF_BUSY, 'b' }, + { TF_BUSY_IN, 'i' }, + { TF_BUSY_OUT, 'o' }, + { 0, '\0'}, }; -- cgit v1.1