From 403bad72b67d8b3f5a0240af5023adfa48132a65 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 30 Apr 2013 15:28:10 -0700 Subject: coredump: only SIGKILL should interrupt the coredumping task There are 2 well known and ancient problems with coredump/signals, and a lot of related bug reports: - do_coredump() clears TIF_SIGPENDING but of course this can't help if, say, SIGCHLD comes after that. In this case the coredump can fail unexpectedly. See for example wait_for_dump_helper()->signal_pending() check but there are other reasons. - At the same time, dumping a huge core on the slow media can take a lot of time/resources and there is no way to kill the coredumping task reliably. In particular this is not oom_kill-friendly. This patch tries to fix the 1st problem, and makes the preparation for the next changes. We add the new SIGNAL_GROUP_COREDUMP flag set by zap_threads() to indicate that this process dumps the core. prepare_signal() checks this flag and nacks any signal except SIGKILL. Note that this check tries to be conservative, in the long term we should probably treat the SIGNAL_GROUP_EXIT case equally but this needs more discussion. See marc.info/?l=linux-kernel&m=120508897917439 Notes: - recalc_sigpending() doesn't check SIGNAL_GROUP_COREDUMP. The patch assumes that dump_write/etc paths should never call it, but we can change it as well. - There is another source of TIF_SIGPENDING, freezer. This will be addressed separately. Signed-off-by: Oleg Nesterov Tested-by: Mandeep Singh Baines Cc: Ingo Molnar Cc: Neil Horman Cc: "Rafael J. Wysocki" Cc: Roland McGrath Cc: Tejun Heo Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/signal.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'kernel/signal.c') diff --git a/kernel/signal.c b/kernel/signal.c index 27ece019bd0a..cede58910f9c 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -854,12 +854,14 @@ static void ptrace_trap_notify(struct task_struct *t) * Returns true if the signal should be actually delivered, otherwise * it should be dropped. */ -static int prepare_signal(int sig, struct task_struct *p, bool force) +static bool prepare_signal(int sig, struct task_struct *p, bool force) { struct signal_struct *signal = p->signal; struct task_struct *t; - if (unlikely(signal->flags & SIGNAL_GROUP_EXIT)) { + if (signal->flags & (SIGNAL_GROUP_EXIT | SIGNAL_GROUP_COREDUMP)) { + if (signal->flags & SIGNAL_GROUP_COREDUMP) + return sig == SIGKILL; /* * The process is in the middle of dying, nothing to do. */ -- cgit v1.2.3