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Date: Wed, 22 May 2019 17:05:06 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Deepa Dinamani <deepa.kernel@...il.com>
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
viro@...iv.linux.org.uk, arnd@...db.de, dbueso@...e.de,
axboe@...nel.dk, dave@...olabs.net, e@...24.org, jbaron@...mai.com,
linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
omar.kilani@...il.com, tglx@...utronix.de, stable@...r.kernel.org
Subject: Re: [PATCH v2] signal: Adjust error codes according to
restore_user_sigmask()
On 05/21, Deepa Dinamani wrote:
>
> Note that this patch returns interrupted errors (EINTR, ERESTARTNOHAND,
> etc) only when there is no other error. If there is a signal and an error
> like EINVAL, the syscalls return -EINVAL rather than the interrupted
> error codes.
Ugh. I need to re-check, but at first glance I really dislike this change.
I think we can fix the problem _and_ simplify the code. Something like below.
The patch is obviously incomplete, it changes only only one caller of
set_user_sigmask(), epoll_pwait() to explain what I mean.
restore_user_sigmask() should simply die. Although perhaps another helper
makes sense to add WARN_ON(test_tsk_restore_sigmask() && !signal_pending).
Oleg.
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 4a0e98d..85f56e4 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2318,19 +2318,19 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
size_t, sigsetsize)
{
int error;
- sigset_t ksigmask, sigsaved;
/*
* If the caller wants a certain signal mask to be set during the wait,
* we apply it here.
*/
- error = set_user_sigmask(sigmask, &ksigmask, &sigsaved, sigsetsize);
+ error = set_user_sigmask(sigmask, sigsetsize);
if (error)
return error;
error = do_epoll_wait(epfd, events, maxevents, timeout);
- restore_user_sigmask(sigmask, &sigsaved);
+ if (error != -EINTR)
+ restore_saved_sigmask();
return error;
}
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index e412c09..1e82ae0 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -416,7 +416,6 @@ void task_join_group_stop(struct task_struct *task);
static inline void set_restore_sigmask(void)
{
set_thread_flag(TIF_RESTORE_SIGMASK);
- WARN_ON(!test_thread_flag(TIF_SIGPENDING));
}
static inline void clear_tsk_restore_sigmask(struct task_struct *tsk)
@@ -447,7 +446,6 @@ static inline bool test_and_clear_restore_sigmask(void)
static inline void set_restore_sigmask(void)
{
current->restore_sigmask = true;
- WARN_ON(!test_thread_flag(TIF_SIGPENDING));
}
static inline void clear_tsk_restore_sigmask(struct task_struct *tsk)
{
diff --git a/include/linux/signal.h b/include/linux/signal.h
index 9702016..887cea6 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -273,8 +273,7 @@ extern int group_send_sig_info(int sig, struct kernel_siginfo *info,
struct task_struct *p, enum pid_type type);
extern int __group_send_sig_info(int, struct kernel_siginfo *, struct task_struct *);
extern int sigprocmask(int, sigset_t *, sigset_t *);
-extern int set_user_sigmask(const sigset_t __user *usigmask, sigset_t *set,
- sigset_t *oldset, size_t sigsetsize);
+extern int set_user_sigmask(const sigset_t __user *umask, size_t sigsetsize);
extern void restore_user_sigmask(const void __user *usigmask,
sigset_t *sigsaved);
extern void set_current_blocked(sigset_t *);
diff --git a/kernel/signal.c b/kernel/signal.c
index 227ba17..76f4f9a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2801,19 +2801,21 @@ EXPORT_SYMBOL(sigprocmask);
* This is useful for syscalls such as ppoll, pselect, io_pgetevents and
* epoll_pwait where a new sigmask is passed from userland for the syscalls.
*/
-int set_user_sigmask(const sigset_t __user *usigmask, sigset_t *set,
- sigset_t *oldset, size_t sigsetsize)
+int set_user_sigmask(const sigset_t __user *umask, size_t sigsetsize)
{
- if (!usigmask)
+ sigset_t *kmask;
+
+ if (!umask)
return 0;
if (sigsetsize != sizeof(sigset_t))
return -EINVAL;
- if (copy_from_user(set, usigmask, sizeof(sigset_t)))
+ if (copy_from_user(kmask, umask, sizeof(sigset_t)))
return -EFAULT;
- *oldset = current->blocked;
- set_current_blocked(set);
+ set_restore_sigmask();
+ current->saved_sigmask = current->blocked;
+ set_current_blocked(kmask);
return 0;
}
@@ -2840,39 +2842,6 @@ int set_compat_user_sigmask(const compat_sigset_t __user *usigmask,
EXPORT_SYMBOL(set_compat_user_sigmask);
#endif
-/*
- * restore_user_sigmask:
- * usigmask: sigmask passed in from userland.
- * sigsaved: saved sigmask when the syscall started and changed the sigmask to
- * usigmask.
- *
- * This is useful for syscalls such as ppoll, pselect, io_pgetevents and
- * epoll_pwait where a new sigmask is passed in from userland for the syscalls.
- */
-void restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved)
-{
-
- if (!usigmask)
- return;
- /*
- * When signals are pending, do not restore them here.
- * Restoring sigmask here can lead to delivering signals that the above
- * syscalls are intended to block because of the sigmask passed in.
- */
- if (signal_pending(current)) {
- current->saved_sigmask = *sigsaved;
- set_restore_sigmask();
- return;
- }
-
- /*
- * This is needed because the fast syscall return path does not restore
- * saved_sigmask when signals are not pending.
- */
- set_current_blocked(sigsaved);
-}
-EXPORT_SYMBOL(restore_user_sigmask);
-
/**
* sys_rt_sigprocmask - change the list of currently blocked signals
* @how: whether to add, remove, or set signals
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