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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
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;
}
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) {