linux/fs/signalfd.c
Oleg Nesterov d80e731eca epoll: introduce POLLFREE to flush ->signalfd_wqh before kfree()
This patch is intentionally incomplete to simplify the review.
It ignores ep_unregister_pollwait() which plays with the same wqh.
See the next change.

epoll assumes that the EPOLL_CTL_ADD'ed file controls everything
f_op->poll() needs. In particular it assumes that the wait queue
can't go away until eventpoll_release(). This is not true in case
of signalfd, the task which does EPOLL_CTL_ADD uses its ->sighand
which is not connected to the file.

This patch adds the special event, POLLFREE, currently only for
epoll. It expects that init_poll_funcptr()'ed hook should do the
necessary cleanup. Perhaps it should be defined as EPOLLFREE in
eventpoll.

__cleanup_sighand() is changed to do wake_up_poll(POLLFREE) if
->signalfd_wqh is not empty, we add the new signalfd_cleanup()
helper.

ep_poll_callback(POLLFREE) simply does list_del_init(task_list).
This make this poll entry inconsistent, but we don't care. If you
share epoll fd which contains our sigfd with another process you
should blame yourself. signalfd is "really special". I simply do
not know how we can define the "right" semantics if it used with
epoll.

The main problem is, epoll calls signalfd_poll() once to establish
the connection with the wait queue, after that signalfd_poll(NULL)
returns the different/inconsistent results depending on who does
EPOLL_CTL_MOD/signalfd_read/etc. IOW: apart from sigmask, signalfd
has nothing to do with the file, it works with the current thread.

In short: this patch is the hack which tries to fix the symptoms.
It also assumes that nobody can take tasklist_lock under epoll
locks, this seems to be true.

Note:

	- we do not have wake_up_all_poll() but wake_up_poll()
	  is fine, poll/epoll doesn't use WQ_FLAG_EXCLUSIVE.

	- signalfd_cleanup() uses POLLHUP along with POLLFREE,
	  we need a couple of simple changes in eventpoll.c to
	  make sure it can't be "lost".

Reported-by: Maxime Bizon <mbizon@freebox.fr>
Cc: <stable@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-02-24 11:42:50 -08:00

292 lines
7.8 KiB
C

/*
* fs/signalfd.c
*
* Copyright (C) 2003 Linus Torvalds
*
* Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
* Changed ->read() to return a siginfo strcture instead of signal number.
* Fixed locking in ->poll().
* Added sighand-detach notification.
* Added fd re-use in sys_signalfd() syscall.
* Now using anonymous inode source.
* Thanks to Oleg Nesterov for useful code review and suggestions.
* More comments and suggestions from Arnd Bergmann.
* Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
* Retrieve multiple signals with one read() call
* Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
* Attach to the sighand only during read() and poll().
*/
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/list.h>
#include <linux/anon_inodes.h>
#include <linux/signalfd.h>
#include <linux/syscalls.h>
void signalfd_cleanup(struct sighand_struct *sighand)
{
wait_queue_head_t *wqh = &sighand->signalfd_wqh;
if (likely(!waitqueue_active(wqh)))
return;
/* wait_queue_t->func(POLLFREE) should do remove_wait_queue() */
wake_up_poll(wqh, POLLHUP | POLLFREE);
}
struct signalfd_ctx {
sigset_t sigmask;
};
static int signalfd_release(struct inode *inode, struct file *file)
{
kfree(file->private_data);
return 0;
}
static unsigned int signalfd_poll(struct file *file, poll_table *wait)
{
struct signalfd_ctx *ctx = file->private_data;
unsigned int events = 0;
poll_wait(file, &current->sighand->signalfd_wqh, wait);
spin_lock_irq(&current->sighand->siglock);
if (next_signal(&current->pending, &ctx->sigmask) ||
next_signal(&current->signal->shared_pending,
&ctx->sigmask))
events |= POLLIN;
spin_unlock_irq(&current->sighand->siglock);
return events;
}
/*
* Copied from copy_siginfo_to_user() in kernel/signal.c
*/
static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
siginfo_t const *kinfo)
{
long err;
BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
/*
* Unused members should be zero ...
*/
err = __clear_user(uinfo, sizeof(*uinfo));
/*
* If you change siginfo_t structure, please be sure
* this code is fixed accordingly.
*/
err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
switch (kinfo->si_code & __SI_MASK) {
case __SI_KILL:
err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
break;
case __SI_TIMER:
err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
break;
case __SI_POLL:
err |= __put_user(kinfo->si_band, &uinfo->ssi_band);
err |= __put_user(kinfo->si_fd, &uinfo->ssi_fd);
break;
case __SI_FAULT:
err |= __put_user((long) kinfo->si_addr, &uinfo->ssi_addr);
#ifdef __ARCH_SI_TRAPNO
err |= __put_user(kinfo->si_trapno, &uinfo->ssi_trapno);
#endif
#ifdef BUS_MCEERR_AO
/*
* Other callers might not initialize the si_lsb field,
* so check explicitly for the right codes here.
*/
if (kinfo->si_code == BUS_MCEERR_AR ||
kinfo->si_code == BUS_MCEERR_AO)
err |= __put_user((short) kinfo->si_addr_lsb,
&uinfo->ssi_addr_lsb);
#endif
break;
case __SI_CHLD:
err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
err |= __put_user(kinfo->si_status, &uinfo->ssi_status);
err |= __put_user(kinfo->si_utime, &uinfo->ssi_utime);
err |= __put_user(kinfo->si_stime, &uinfo->ssi_stime);
break;
case __SI_RT: /* This is not generated by the kernel as of now. */
case __SI_MESGQ: /* But this is */
err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
break;
default:
/*
* This case catches also the signals queued by sigqueue().
*/
err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
break;
}
return err ? -EFAULT: sizeof(*uinfo);
}
static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
int nonblock)
{
ssize_t ret;
DECLARE_WAITQUEUE(wait, current);
spin_lock_irq(&current->sighand->siglock);
ret = dequeue_signal(current, &ctx->sigmask, info);
switch (ret) {
case 0:
if (!nonblock)
break;
ret = -EAGAIN;
default:
spin_unlock_irq(&current->sighand->siglock);
return ret;
}
add_wait_queue(&current->sighand->signalfd_wqh, &wait);
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
ret = dequeue_signal(current, &ctx->sigmask, info);
if (ret != 0)
break;
if (signal_pending(current)) {
ret = -ERESTARTSYS;
break;
}
spin_unlock_irq(&current->sighand->siglock);
schedule();
spin_lock_irq(&current->sighand->siglock);
}
spin_unlock_irq(&current->sighand->siglock);
remove_wait_queue(&current->sighand->signalfd_wqh, &wait);
__set_current_state(TASK_RUNNING);
return ret;
}
/*
* Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
* error code. The "count" parameter must be at least the size of a
* "struct signalfd_siginfo".
*/
static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
loff_t *ppos)
{
struct signalfd_ctx *ctx = file->private_data;
struct signalfd_siginfo __user *siginfo;
int nonblock = file->f_flags & O_NONBLOCK;
ssize_t ret, total = 0;
siginfo_t info;
count /= sizeof(struct signalfd_siginfo);
if (!count)
return -EINVAL;
siginfo = (struct signalfd_siginfo __user *) buf;
do {
ret = signalfd_dequeue(ctx, &info, nonblock);
if (unlikely(ret <= 0))
break;
ret = signalfd_copyinfo(siginfo, &info);
if (ret < 0)
break;
siginfo++;
total += ret;
nonblock = 1;
} while (--count);
return total ? total: ret;
}
static const struct file_operations signalfd_fops = {
.release = signalfd_release,
.poll = signalfd_poll,
.read = signalfd_read,
.llseek = noop_llseek,
};
SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
size_t, sizemask, int, flags)
{
sigset_t sigmask;
struct signalfd_ctx *ctx;
/* Check the SFD_* constants for consistency. */
BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
return -EINVAL;
if (sizemask != sizeof(sigset_t) ||
copy_from_user(&sigmask, user_mask, sizeof(sigmask)))
return -EINVAL;
sigdelsetmask(&sigmask, sigmask(SIGKILL) | sigmask(SIGSTOP));
signotset(&sigmask);
if (ufd == -1) {
ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return -ENOMEM;
ctx->sigmask = sigmask;
/*
* When we call this, the initialization must be complete, since
* anon_inode_getfd() will install the fd.
*/
ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
if (ufd < 0)
kfree(ctx);
} else {
struct file *file = fget(ufd);
if (!file)
return -EBADF;
ctx = file->private_data;
if (file->f_op != &signalfd_fops) {
fput(file);
return -EINVAL;
}
spin_lock_irq(&current->sighand->siglock);
ctx->sigmask = sigmask;
spin_unlock_irq(&current->sighand->siglock);
wake_up(&current->sighand->signalfd_wqh);
fput(file);
}
return ufd;
}
SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
size_t, sizemask)
{
return sys_signalfd4(ufd, user_mask, sizemask, 0);
}