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coredump: only SIGKILL should interrupt the coredumping task

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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>
This commit is contained in:
Oleg Nesterov 2013-04-30 15:28:10 -07:00 • committed by Linus Torvalds
parent 66e5b7e194
commit 403bad72b6
3 changed files with 10 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
fs/coredump.c
View file

@ -280,8 +280,8 @@ static int zap_process(struct task_struct *start, int exit_code)
return nr; 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 core_state *core_state, int exit_code)
{ {
struct task_struct *g, *p; struct task_struct *g, *p;
unsigned long flags; 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)) { if (!signal_group_exit(tsk->signal)) {
mm->core_state = core_state; mm->core_state = core_state;
nr = zap_process(tsk, exit_code); 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); spin_unlock_irq(&tsk->sighand->siglock);
if (unlikely(nr < 0)) if (unlikely(nr < 0))
@ -514,12 +517,6 @@ void do_coredump(siginfo_t *siginfo)
old_cred = override_creds(cred); 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); ispipe = format_corename(&cn, &cprm);
if (ispipe) { if (ispipe) {

1
include/linux/sched.h
View file

@ -626,6 +626,7 @@ struct signal_struct {
#define SIGNAL_STOP_STOPPED 0x00000001 /* job control stop in effect */ #define SIGNAL_STOP_STOPPED 0x00000001 /* job control stop in effect */
#define SIGNAL_STOP_CONTINUED 0x00000002 /* SIGCONT since WCONTINUED reap */ #define SIGNAL_STOP_CONTINUED 0x00000002 /* SIGCONT since WCONTINUED reap */
#define SIGNAL_GROUP_EXIT 0x00000004 /* group exit in progress */ #define SIGNAL_GROUP_EXIT 0x00000004 /* group exit in progress */
#define SIGNAL_GROUP_COREDUMP 0x00000008 /* coredump in progress */
/* /*
* Pending notifications to parent. * Pending notifications to parent.
*/ */

6
kernel/signal.c
View file

@ -854,12 +854,14 @@ static void ptrace_trap_notify(struct task_struct *t)
* Returns true if the signal should be actually delivered, otherwise * Returns true if the signal should be actually delivered, otherwise
* it should be dropped. * 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 signal_struct *signal = p->signal;
struct task_struct *t; 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. * The process is in the middle of dying, nothing to do.
*/ */