From 6e94dbc7a4e49a028b81302d755bba1a518f973b Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Wed, 5 May 2021 11:19:05 +0200 Subject: tty: cumulate and document tty_struct::flow* members Group the flow flags under a single struct called flow. The new struct contains 'stopped' and 'tco_stopped' bools which used to be bits in a bitfield. The struct also contains the lock protecting them to potentially share the same cache line. Note that commit c545b66c6922b (tty: Serialize tcflow() with other tty flow control changes) added a padding to the original bitfield. It was for the bitfield to occupy a whole 64b word to avoid interferring stores on Alpha (cannot we evaporate this arch with weird implications to C code yet?). But it doesn't work as expected as the padding (tty_struct::unused) is aligned to a 8B boundary too and occupies some bytes from the next word. So make it reliable by: 1) setting __aligned of the struct -- that aligns the start, and 2) making 'unsigned long unused[0]' as the last member of the struct -- pads the end. This is also the perfect time to start the documentation of tty_struct where all this lives. So we start by documenting what these bools actually serve for. And why we do all the alignment dances. Only the few up-to-date information from the Theodore's comment made it into this new Kerneldoc comment. Signed-off-by: Jiri Slaby Cc: "David S. Miller" Cc: Jakub Kicinski Cc: Jonathan Corbet Cc: Arnd Bergmann Cc: Ulf Hansson Cc: Heiko Carstens Cc: Vasily Gorbik Cc: Christian Borntraeger Cc: Shawn Guo Cc: Sascha Hauer Cc: Vineet Gupta Cc: "Maciej W. Rozycki" Link: https://lore.kernel.org/r/20210505091928.22010-13-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman --- include/linux/tty.h | 38 ++++++++++++++++++++++---------------- 1 file changed, 22 insertions(+), 16 deletions(-) (limited to 'include/linux/tty.h') diff --git a/include/linux/tty.h b/include/linux/tty.h index 5aad2220266c..df3a69b2e1ea 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -243,20 +243,22 @@ struct tty_port { #define TTY_PORT_KOPENED 5 /* device exclusively opened by kernel */ -/* - * Where all of the state associated with a tty is kept while the tty - * is open. Since the termios state should be kept even if the tty - * has been closed --- for things like the baud rate, etc --- it is - * not stored here, but rather a pointer to the real state is stored - * here. Possible the winsize structure should have the same - * treatment, but (1) the default 80x24 is usually right and (2) it's - * most often used by a windowing system, which will set the correct - * size each time the window is created or resized anyway. - * - TYT, 9/14/92 - */ - struct tty_operations; +/** + * struct tty_struct - state associated with a tty while open + * + * @flow.lock: lock for flow members + * @flow.stopped: tty stopped/started by tty_stop/tty_start + * @flow.tco_stopped: tty stopped/started by TCOOFF/TCOON ioctls (it has + * precedense over @flow.stopped) + * @flow.unused: alignment for Alpha, so that no members other than @flow.* are + * modified by the same 64b word store. The @flow's __aligned is + * there for the very same reason. + * + * All of the state associated with a tty while the tty is open. Persistent + * storage for tty devices is referenced here as @port in struct tty_port. + */ struct tty_struct { int magic; struct kref kref; @@ -275,7 +277,6 @@ struct tty_struct { struct rw_semaphore termios_rwsem; struct mutex winsize_mutex; spinlock_t ctrl_lock; - spinlock_t flow_lock; /* Termios values are protected by the termios rwsem */ struct ktermios termios, termios_locked; char name[64]; @@ -288,9 +289,14 @@ struct tty_struct { unsigned long flags; int count; struct winsize winsize; /* winsize_mutex */ - unsigned long stopped:1, /* flow_lock */ - flow_stopped:1, - unused:BITS_PER_LONG - 2; + + struct { + spinlock_t lock; + bool stopped; + bool tco_stopped; + unsigned long unused[0]; + } __aligned(sizeof(unsigned long)) flow; + int hw_stopped; unsigned long ctrl_status:8, /* ctrl_lock */ packet:1, -- cgit