On Tue, 30 May 2017, Thomas Gleixner wrote: > The commit which added the queuing of blocked and ignored signals is in the > history tree with a pretty useless changelog. > > https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git > > commit 98fc8ab9e74389e0c7001052597f61336dc62833 > Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxxx> > Date: Tue Feb 11 20:49:03 2003 -0800 > > Don't wake up processes unnecessarily for ignored signals > > It rewrites sig_ignored() and adds the following to it: > > + /* > + * Blocked signals are never ignored, since the > + * signal handler may change by the time it is > + * unblocked. > + */ > + if (sigismember(&t->blocked, sig)) > + return 0; > > I have no idea how that is related to $subject of the commit and why this > decision was made. > > Linus, any recollection? So I found at least some explanation by studying the spec some more. There are two variants of ignored signals: 1) handler is SIG_IGN 2) handler is SIG_DFL and default action is 'ignore' These are the signals in SIG_KERNEL_IGNORE_MASK #define SIG_KERNEL_IGNORE_MASK (\ rt_sigmask(SIGCONT) | rt_sigmask(SIGCHLD) | \ rt_sigmask(SIGWINCH) | rt_sigmask(SIGURG) ) These signals are not allowed to be discarded when the signal is blocked. So my understanding of the spec is: #1 Can discard the signals as long as SIG_IGN is set whether the signal is blocked or not #2 Must queue them if the signal is blocked, otherwise discard I changed the logic according to this with the patch below and a quick test run of lpt and glibc test cases produces no failures. Thoughts? Thanks, tglx 8<-------------------- Subject: signals: Reduce scope of blocked signals in sig_handler_ignored() From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Date: Tue, 30 May 2017 18:01:33 +0200 Add proper changelog and a big fat comment in the code. Not-yet-signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> --- kernel/signal.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) Index: b/kernel/signal.c =================================================================== --- a/kernel/signal.c +++ b/kernel/signal.c @@ -70,6 +70,13 @@ static int sig_handler_ignored(void __us (handler == SIG_DFL && sig_kernel_ignore(sig)); } +static int sig_handler_is_sigign(struct task_struct *t, int sig) +{ + void __user *handler = sig_handler(t, sig); + + return handler == SIG_IGN; +} + static int sig_task_ignored(struct task_struct *t, int sig, bool force) { void __user *handler; @@ -91,7 +98,7 @@ static int sig_ignored(struct task_struc * unblocked. */ if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig)) - return 0; + return sig_handler_is_sigign(t, sig); if (!sig_task_ignored(t, sig, force)) return 0; -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
