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authorOleg Nesterov <oleg@redhat.com>2013-04-30 15:28:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-04-30 17:04:06 -0700
commit403bad72b67d8b3f5a0240af5023adfa48132a65 (patch)
treed240a287cf7e64824dc6441f397b0290aa79738b /kernel/signal.c
parent66e5b7e1948cdbdca2b0cc6ddc6d69ee84583fb4 (diff)
downloadlinux-403bad72b67d8b3f5a0240af5023adfa48132a65.tar.bz2
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 <oleg@redhat.com> Tested-by: Mandeep Singh Baines <msb@chromium.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Neil Horman <nhorman@redhat.com> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> Cc: Roland McGrath <roland@hack.frob.com> Cc: Tejun Heo <tj@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c6
1 files changed, 4 insertions, 2 deletions
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.
*/