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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
parent66e5b7e1948cdbdca2b0cc6ddc6d69ee84583fb4 (diff)
downloadlinux-403bad72b67d8b3f5a0240af5023adfa48132a65.tar.gz
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>
-rw-r--r--fs/coredump.c13
-rw-r--r--include/linux/sched.h1
-rw-r--r--kernel/signal.c6
3 files changed, 10 insertions, 10 deletions
diff --git a/fs/coredump.c b/fs/coredump.c
index d52f6bd5ad8..f91cfd8cd5f 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -280,8 +280,8 @@ static int zap_process(struct task_struct *start, int exit_code)
return nr;
}
-static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
- struct core_state *core_state, int exit_code)
+static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
+ struct core_state *core_state, int exit_code)
{
struct task_struct *g, *p;
unsigned long flags;
@@ -291,6 +291,9 @@ static inline int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
if (!signal_group_exit(tsk->signal)) {
mm->core_state = core_state;
nr = zap_process(tsk, exit_code);
+ /* ignore all signals except SIGKILL, see prepare_signal() */
+ tsk->signal->flags |= SIGNAL_GROUP_COREDUMP;
+ clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
}
spin_unlock_irq(&tsk->sighand->siglock);
if (unlikely(nr < 0))
@@ -514,12 +517,6 @@ void do_coredump(siginfo_t *siginfo)
old_cred = override_creds(cred);
- /*
- * Clear any false indication of pending signals that might
- * be seen by the filesystem code called to write the core file.
- */
- clear_thread_flag(TIF_SIGPENDING);
-
ispipe = format_corename(&cn, &cprm);
if (ispipe) {
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 54ddcb82cdd..a22baf83c20 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -626,6 +626,7 @@ struct signal_struct {
#define SIGNAL_STOP_STOPPED 0x00000001 /* job control stop in effect */
#define SIGNAL_STOP_CONTINUED 0x00000002 /* SIGCONT since WCONTINUED reap */
#define SIGNAL_GROUP_EXIT 0x00000004 /* group exit in progress */
+#define SIGNAL_GROUP_COREDUMP 0x00000008 /* coredump in progress */
/*
* Pending notifications to parent.
*/
diff --git a/kernel/signal.c b/kernel/signal.c
index 27ece019bd0..cede58910f9 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.
*/