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Date: Tue, 25 Jun 2013 17:05:37 +0200
From: Denys Vlasenko <dvlasenk@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Denys Vlasenko <dvlasenk@...hat.com>,
Oleg Nesterov <oleg@...hat.com>
Subject: [PATCH] epoll_[p]wait: fix spurious -EINTR on ptrace attach
Before this change, epoll_wait and epoll_pwait
spuriously return with -EINTR on ptrace attach.
By analogy with poll syscall family, epoll_[p]wait should be interruptible
by signals regardless of SA_RESTART, therefore, this change
makes them return -ERESTARTNOHAND if timeout has expired.
If timeout has not expired, and if interrupted by harmless SIG_DFL'ed
signals such as SIGWINCH and other signal-like activity
such as ptrace attach, epoll_[p]wait should restart with decreased timeout.
To that end, set up restart block and return -ERESTART_RESTARTBLOCK.
In order to define a "sigset_t ksigmask" member, I had to add
<asm/signal.h> to linux/thread_info.h, which threw some
build errors about undefined smp barriers and such.
Removing <linux/seqlock.h> include from linux/time.h
solved it.
Run-tested.
Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Oleg Nesterov <oleg@...hat.com>
---
fs/eventpoll.c | 146 ++++++++++++++++++++++++++------------------
include/linux/thread_info.h | 10 +++
include/linux/time.h | 1 -
3 files changed, 98 insertions(+), 59 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 0cff4434..1df35aa 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1911,16 +1911,16 @@ error_return:
return error;
}
-/*
- * Implement the event wait interface for the eventpoll file. It is the kernel
- * part of the user space epoll_wait(2).
- */
-SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
- int, maxevents, int, timeout)
+static long do_restart_epoll_pwait(struct restart_block *restart_block);
+
+static long do_epoll_pwait(int epfd, struct epoll_event __user *events,
+ int maxevents, int timeout, const sigset_t *sigmask)
{
int error;
+ sigset_t ksigmask, ksigsaved;
struct fd f;
struct eventpoll *ep;
+ struct timespec start;
/* The maximum number of event must be greater than zero */
if (maxevents <= 0 || maxevents > EP_MAX_EVENTS)
@@ -1944,19 +1944,97 @@ SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
goto error_fput;
/*
+ * If the caller wants a certain signal mask to be set during the wait,
+ * we apply it here.
+ */
+ if (sigmask) {
+ ksigmask = *sigmask;
+ sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
+ sigprocmask(SIG_SETMASK, &ksigmask, &ksigsaved);
+ }
+
+ /*
* At this point it is safe to assume that the "private_data" contains
* our own data structure.
*/
ep = f.file->private_data;
+ if (timeout > 0)
+ ktime_get_ts(&start);
+
/* Time to fish for events ... */
error = ep_poll(ep, events, maxevents, timeout);
+ if (error == -EINTR) {
+ error = -ERESTARTNOHAND;
+ if (timeout > 0) {
+ struct restart_block *restart_block;
+ struct timespec end;
+ ktime_t rem;
+ s64 rem_msec;
+
+ ktime_get_ts(&end);
+ rem = ktime_sub(timespec_to_ktime(end), timespec_to_ktime(start));
+ rem_msec = ktime_to_ms(rem);
+ if (rem_msec > 0) {
+ restart_block = ¤t_thread_info()->restart_block;
+ restart_block->fn = do_restart_epoll_pwait;
+ restart_block->epoll.epfd = epfd;
+ restart_block->epoll.events = events;
+ restart_block->epoll.maxevents = maxevents;
+ restart_block->epoll.timeout = rem_msec;
+ restart_block->epoll.has_ksigmask = (sigmask != NULL);
+ restart_block->epoll.ksigmask = ksigmask;
+ error = -ERESTART_RESTARTBLOCK;
+ }
+ }
+ /*
+ * We've got a signal while waiting, we do not restore the
+ * signal mask yet, and we allow do_signal() to deliver the signal on
+ * the way back to userspace, before the signal mask is restored.
+ */
+ if (sigmask) {
+ memcpy(¤t->saved_sigmask, &ksigsaved,
+ sizeof(ksigsaved));
+ set_restore_sigmask();
+ }
+ }
+ else
+ /*
+ * If we changed the signal mask, we need to restore the original one.
+ */
+ if (sigmask) {
+ sigprocmask(SIG_SETMASK, &ksigsaved, NULL);
+ }
+
error_fput:
fdput(f);
return error;
}
+static long do_restart_epoll_pwait(struct restart_block *restart_block)
+{
+ int epfd = restart_block->epoll.epfd;
+ struct epoll_event __user *events = restart_block->epoll.events;
+ int maxevents = restart_block->epoll.maxevents;
+ int timeout = restart_block->epoll.timeout;
+ sigset_t *ksigmask = restart_block->epoll.has_ksigmask
+ ? &restart_block->epoll.ksigmask
+ : NULL;
+
+ return do_epoll_pwait(epfd, events, maxevents, timeout, ksigmask);
+}
+
+/*
+ * Implement the event wait interface for the eventpoll file. It is the kernel
+ * part of the user space epoll_wait(2).
+ */
+SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events,
+ int, maxevents, int, timeout)
+{
+ return do_epoll_pwait(epfd, events, maxevents, timeout, NULL);
+}
+
/*
* Implement the event wait interface for the eventpoll file. It is the kernel
* part of the user space epoll_pwait(2).
@@ -1965,40 +2043,16 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
int, maxevents, int, timeout, const sigset_t __user *, sigmask,
size_t, sigsetsize)
{
- int error;
- sigset_t ksigmask, sigsaved;
+ sigset_t ksigmask;
- /*
- * If the caller wants a certain signal mask to be set during the wait,
- * we apply it here.
- */
if (sigmask) {
if (sigsetsize != sizeof(sigset_t))
return -EINVAL;
if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
return -EFAULT;
- sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
- sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
}
- error = sys_epoll_wait(epfd, events, maxevents, timeout);
-
- /*
- * If we changed the signal mask, we need to restore the original one.
- * In case we've got a signal while waiting, we do not restore the
- * signal mask yet, and we allow do_signal() to deliver the signal on
- * the way back to userspace, before the signal mask is restored.
- */
- if (sigmask) {
- if (error == -EINTR) {
- memcpy(¤t->saved_sigmask, &sigsaved,
- sizeof(sigsaved));
- set_restore_sigmask();
- } else
- sigprocmask(SIG_SETMASK, &sigsaved, NULL);
- }
-
- return error;
+ return do_epoll_pwait(epfd, events, maxevents, timeout, sigmask ? &ksigmask : NULL);
}
#ifdef CONFIG_COMPAT
@@ -2008,42 +2062,18 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
const compat_sigset_t __user *, sigmask,
compat_size_t, sigsetsize)
{
- long err;
compat_sigset_t csigmask;
- sigset_t ksigmask, sigsaved;
+ sigset_t ksigmask;
- /*
- * If the caller wants a certain signal mask to be set during the wait,
- * we apply it here.
- */
if (sigmask) {
if (sigsetsize != sizeof(compat_sigset_t))
return -EINVAL;
if (copy_from_user(&csigmask, sigmask, sizeof(csigmask)))
return -EFAULT;
sigset_from_compat(&ksigmask, &csigmask);
- sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
- sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
- }
-
- err = sys_epoll_wait(epfd, events, maxevents, timeout);
-
- /*
- * If we changed the signal mask, we need to restore the original one.
- * In case we've got a signal while waiting, we do not restore the
- * signal mask yet, and we allow do_signal() to deliver the signal on
- * the way back to userspace, before the signal mask is restored.
- */
- if (sigmask) {
- if (err == -EINTR) {
- memcpy(¤t->saved_sigmask, &sigsaved,
- sizeof(sigsaved));
- set_restore_sigmask();
- } else
- sigprocmask(SIG_SETMASK, &sigsaved, NULL);
}
- return err;
+ return do_epoll_pwait(epfd, events, maxevents, timeout, sigmask ? &ksigmask : NULL);
}
#endif
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index e7e0473..1a7e0c6 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -8,6 +8,7 @@
#define _LINUX_THREAD_INFO_H
#include <linux/types.h>
+#include <asm/signal.h>
#include <linux/bug.h>
struct timespec;
@@ -45,6 +46,15 @@ struct restart_block {
unsigned long tv_sec;
unsigned long tv_nsec;
} poll;
+ /* For epoll_[p]wait */
+ struct {
+ int epfd;
+ int maxevents;
+ int timeout;
+ int has_ksigmask;
+ struct epoll_event __user *events;
+ sigset_t ksigmask;
+ } epoll;
};
};
diff --git a/include/linux/time.h b/include/linux/time.h
index d5d229b..f0c1152 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -2,7 +2,6 @@
#define _LINUX_TIME_H
# include <linux/cache.h>
-# include <linux/seqlock.h>
# include <linux/math64.h>
#include <uapi/linux/time.h>
--
1.8.1.4
--
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