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author | Oleg Nesterov <oleg@redhat.com> | 2013-04-30 15:28:10 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-04-30 17:04:06 -0700 |
commit | 403bad72b67d8b3f5a0240af5023adfa48132a65 (patch) | |
tree | d240a287cf7e64824dc6441f397b0290aa79738b | |
parent | 66e5b7e1948cdbdca2b0cc6ddc6d69ee84583fb4 (diff) | |
download | linux-3.10-403bad72b67d8b3f5a0240af5023adfa48132a65.tar.gz linux-3.10-403bad72b67d8b3f5a0240af5023adfa48132a65.tar.bz2 linux-3.10-403bad72b67d8b3f5a0240af5023adfa48132a65.zip |
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.c | 13 | ||||
-rw-r--r-- | include/linux/sched.h | 1 | ||||
-rw-r--r-- | kernel/signal.c | 6 |
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. */ |