coredump: only SIGKILL should interrupt the coredumping task (403bad72) · Commits · 戴 / test

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>

fs/coredump.c

+5 −8

Original line number	Diff line number	Diff line
		@@ -280,7 +280,7 @@ 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,
		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;
		@@ -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) {

include/linux/sched.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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.
		*/

kernel/signal.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -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.
		*/

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