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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 <[email protected]>
Tested-by: Mandeep Singh Baines <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Neil Horman <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Roland McGrath <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Al Viro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Oleg Nesterov 2013-04-30 15:28:10 -07:00 • committed by Linus Torvalds
commit 403bad72b6
3 changed files with 10 additions and 10 deletions
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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
* 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.
*/