linux-toradex.git - Linux kernel for Apalis, Colibri and Verdin modules

Age	Commit message (Collapse)	Author
2011-03-22	tty: stop using "delayed_work" in the tty layer	Linus Torvalds
	Using delayed-work for tty flip buffers ends up causing us to wait for the next tick to complete some actions. That's usually not all that noticeable, but for certain latency-critical workloads it ends up being totally unacceptable. As an extreme case of this, passing a token back-and-forth over a pty will take two ticks per iteration, so even just a thousand iterations will take 8 seconds assuming a common 250Hz configuration. Avoiding the whole delayed work issue brings that ping-pong test-case down to 0.009s on my machine. In more practical terms, this latency has been a performance problem for things like dive computer simulators (simulating the serial interface using the ptys) and for other environments (Alan mentions a CP/M emulator). Reported-by: Jef Driesen <jefdriesen@telenet.be> Acked-by: Greg KH <gregkh@suse.de> Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-11-09	tty: prevent DOS in the flush_to_ldisc	Jiri Olsa
	There's a small window inside the flush_to_ldisc function, where the tty is unlocked and calling ldisc's receive_buf function. If in this window new buffer is added to the tty, the processing might never leave the flush_to_ldisc function. This scenario will hog the cpu, causing other tty processing starving, and making it impossible to interface the computer via tty. I was able to exploit this via pty interface by sending only control characters to the master input, causing the flush_to_ldisc to be scheduled, but never actually generate any output. To reproduce, please run multiple instances of following code. - SNIP #define _XOPEN_SOURCE #include <stdlib.h> #include <stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int main(int argc, char **argv) { int i, slave, master = getpt(); char buf[8192]; sprintf(buf, "%s", ptsname(master)); grantpt(master); unlockpt(master); slave = open(buf, O_RDWR); if (slave < 0) { perror("open slave failed"); return 1; } for(i = 0; i < sizeof(buf); i++) buf[i] = rand() % 32; while(1) { write(master, buf, sizeof(buf)); } return 0; } - SNIP The attached patch (based on -next tree) fixes this by checking on the tty buffer tail. Once it's reached, the current work is rescheduled and another could run. Signed-off-by: Jiri Olsa <jolsa@redhat.com> Cc: stable <stable@kernel.org> Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2010-11-05	TTY: create drivers/tty and move the tty core files there	Greg Kroah-Hartman
	The tty code should be in its own subdirectory and not in the char driver with all of the cruft that is currently there. Based on work done by Arnd Bergmann <arnd@arndb.de> Acked-by: Arnd Bergmann <arnd@arndb.de> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>