signal: don't remove SIGNAL_UNKILLABLE for traced tasks.
PATCH 1/1 signal: don't remove SIGNAL_UNKILLABLE for traced tasks.
When forcing a signal, SIGNAL_UNKILLABLE is removed to prevent recursive faults, but this is undesirable when tracing. For example, debugging an init process (whether global or namespace), hitting a breakpoint and SIGTRAP will force SIGTRAP and then remove SIGNAL_UNKILLABLE. Everything continues fine, but then once debugging has finished, the init process is left killable which is unlikely what the user expects, resulting in either an accidentally killed init or an init that stops reaping zombies.
--- kernel/signal.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
kernel/signal.c +5 -1
@@ -1185,7 +1185,11 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t)recalc_sigpending_and_wake (t); } } -if (action->sa.sa_handler ==SIG_DFL ) +/* +* Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect +* debugging to leave init killable. +*/ +if (action->sa.sa_handler ==SIG_DFL && !t->ptrace) t->signal->flags &= ~SIGNAL_UNKILLABLE ; ret =specific_send_sig_info (sig, info, t);spin_unlock_irqrestore (&t->sighand->siglock, flags);
Signature · 1 line
2.12.0.rc0
Hi Jamie,
I am sorry for being slow... yes, probably we should start with this simple change, and perhaps we do not really need anything else. But let me think about this till Monday, perhaps we can remove this "clear SIGNAL_UNKILLABLE" logic in force_sig_info() altogether.
Quoted 37 lines · Jamie Iles
When forcing a signal,
SIGNAL_UNKILLABLEis removed to prevent recursive faults, but this is undesirable when tracing. For example, debugging an init process (whether global or namespace), hitting a breakpoint and SIGTRAP will force SIGTRAP and then removeSIGNAL_UNKILLABLE. Everything continues fine, but then once debugging has finished, the init process is left killable which is unlikely what the user expects, resulting in either an accidentally killed init or an init that stops reaping zombies.Cc Andrew Morton <[email protected]>Cc Oleg Nesterov <[email protected]>Signed-off-by Jamie Iles <[email protected]>--- kernel/signal.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)kernel/signal.c +5
-1@@ -1185,7 +1185,11 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t)recalc_sigpending_and_wake (t); } } -if (action->sa.sa_handler ==SIG_DFL ) +/* +* Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect +* debugging to leave init killable. +*/ +if (action->sa.sa_handler ==SIG_DFL && !t->ptrace) t->signal->flags &= ~SIGNAL_UNKILLABLE ; ret =specific_send_sig_info (sig, info, t);spin_unlock_irqrestore (&t->sighand->siglock, flags);Signature · 1 line
2.12.0.rc0
Hi Oleg,
Quoted 4 lines · Oleg Nesterov
I am sorry for being slow... yes, probably we should start with this simple change, and perhaps we do not really need anything else. But let me think about this till Monday, perhaps we can remove this "clear
SIGNAL_UNKILLABLE" logic inforce_sig_info()altogether.
No problem, I sent the patch to keep it on my own radar :)
Jamie
Hi Oleg,
Quoted 6 lines · Oleg Nesterov
Hi Jamie,
I am sorry for being slow... yes, probably we should start with this simple change, and perhaps we do not really need anything else. But let me think about this till Monday, perhaps we can remove this "clear
SIGNAL_UNKILLABLE" logic inforce_sig_info()altogether.
I was wondering if you had given this any more thought?
Thanks,
Jamie
Quoted 39 lines · Jamie Iles
Quoted 37 lines
When forcing a signal,
SIGNAL_UNKILLABLEis removed to prevent recursive faults, but this is undesirable when tracing. For example, debugging an init process (whether global or namespace), hitting a breakpoint and SIGTRAP will force SIGTRAP and then removeSIGNAL_UNKILLABLE. Everything continues fine, but then once debugging has finished, the init process is left killable which is unlikely what the user expects, resulting in either an accidentally killed init or an init that stops reaping zombies.Cc Andrew Morton <[email protected]>Cc Oleg Nesterov <[email protected]>Signed-off-by Jamie Iles <[email protected]>--- kernel/signal.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)kernel/signal.c +5
-1@@ -1185,7 +1185,11 @@ force_sig_info(int sig, struct siginfo *info, struct task_struct *t)recalc_sigpending_and_wake (t); } } -if (action->sa.sa_handler ==SIG_DFL ) +/* +* Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect +* debugging to leave init killable. +*/ +if (action->sa.sa_handler ==SIG_DFL && !t->ptrace) t->signal->flags &= ~SIGNAL_UNKILLABLE ; ret =specific_send_sig_info (sig, info, t);spin_unlock_irqrestore (&t->sighand->siglock, flags);Signature · 1 line
2.12.0.rc0