linux/fs/signalfd.c
Oleg Nesterov f9ee228bdc signalfd: make it group-wide, fix posix-timers scheduling
With this patch any thread can dequeue its own private signals via signalfd,
even if it was created by another sub-thread.

To do so, we pass "current" to dequeue_signal() if the caller is from the same
thread group. This also fixes the scheduling of posix timers broken by the
previous patch.

If the caller doesn't belong to this thread group, we can't handle __SI_TIMER
case properly anyway. Perhaps we should forbid the cross-process signalfd usage
and convert ctx->tsk to ctx->sighand.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Roland McGrath <roland@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-08-22 19:52:46 -07:00

386 lines
9.6 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
*/
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/list.h>
#include <linux/anon_inodes.h>
#include <linux/signalfd.h>
struct signalfd_ctx {
struct list_head lnk;
wait_queue_head_t wqh;
sigset_t sigmask;
struct task_struct *tsk;
};
struct signalfd_lockctx {
struct task_struct *tsk;
unsigned long flags;
};
/*
* Tries to acquire the sighand lock. We do not increment the sighand
* use count, and we do not even pin the task struct, so we need to
* do it inside an RCU read lock, and we must be prepared for the
* ctx->tsk going to NULL (in signalfd_deliver()), and for the sighand
* being detached. We return 0 if the sighand has been detached, or
* 1 if we were able to pin the sighand lock.
*/
static int signalfd_lock(struct signalfd_ctx *ctx, struct signalfd_lockctx *lk)
{
struct sighand_struct *sighand = NULL;
rcu_read_lock();
lk->tsk = rcu_dereference(ctx->tsk);
if (likely(lk->tsk != NULL))
sighand = lock_task_sighand(lk->tsk, &lk->flags);
rcu_read_unlock();
if (!sighand)
return 0;
if (!ctx->tsk) {
unlock_task_sighand(lk->tsk, &lk->flags);
return 0;
}
if (lk->tsk->tgid == current->tgid)
lk->tsk = current;
return 1;
}
static void signalfd_unlock(struct signalfd_lockctx *lk)
{
unlock_task_sighand(lk->tsk, &lk->flags);
}
/*
* This must be called with the sighand lock held.
*/
void signalfd_deliver(struct task_struct *tsk, int sig)
{
struct sighand_struct *sighand = tsk->sighand;
struct signalfd_ctx *ctx, *tmp;
BUG_ON(!sig);
list_for_each_entry_safe(ctx, tmp, &sighand->signalfd_list, lnk) {
/*
* We use a negative signal value as a way to broadcast that the
* sighand has been orphaned, so that we can notify all the
* listeners about this. Remember the ctx->sigmask is inverted,
* so if the user is interested in a signal, that corresponding
* bit will be zero.
*/
if (sig < 0) {
if (ctx->tsk == tsk) {
ctx->tsk = NULL;
list_del_init(&ctx->lnk);
wake_up(&ctx->wqh);
}
} else {
if (!sigismember(&ctx->sigmask, sig))
wake_up(&ctx->wqh);
}
}
}
static void signalfd_cleanup(struct signalfd_ctx *ctx)
{
struct signalfd_lockctx lk;
/*
* This is tricky. If the sighand is gone, we do not need to remove
* context from the list, the list itself won't be there anymore.
*/
if (signalfd_lock(ctx, &lk)) {
list_del(&ctx->lnk);
signalfd_unlock(&lk);
}
kfree(ctx);
}
static int signalfd_release(struct inode *inode, struct file *file)
{
signalfd_cleanup(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;
struct signalfd_lockctx lk;
poll_wait(file, &ctx->wqh, wait);
/*
* Let the caller get a POLLIN in this case, ala socket recv() when
* the peer disconnects.
*/
if (signalfd_lock(ctx, &lk)) {
if ((lk.tsk == current &&
next_signal(&lk.tsk->pending, &ctx->sigmask) > 0) ||
next_signal(&lk.tsk->signal->shared_pending,
&ctx->sigmask) > 0)
events |= POLLIN;
signalfd_unlock(&lk);
} else
events |= POLLIN;
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 memebers 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->signo);
err |= __put_user(kinfo->si_errno, &uinfo->err);
err |= __put_user((short)kinfo->si_code, &uinfo->code);
switch (kinfo->si_code & __SI_MASK) {
case __SI_KILL:
err |= __put_user(kinfo->si_pid, &uinfo->pid);
err |= __put_user(kinfo->si_uid, &uinfo->uid);
break;
case __SI_TIMER:
err |= __put_user(kinfo->si_tid, &uinfo->tid);
err |= __put_user(kinfo->si_overrun, &uinfo->overrun);
err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
break;
case __SI_POLL:
err |= __put_user(kinfo->si_band, &uinfo->band);
err |= __put_user(kinfo->si_fd, &uinfo->fd);
break;
case __SI_FAULT:
err |= __put_user((long)kinfo->si_addr, &uinfo->addr);
#ifdef __ARCH_SI_TRAPNO
err |= __put_user(kinfo->si_trapno, &uinfo->trapno);
#endif
break;
case __SI_CHLD:
err |= __put_user(kinfo->si_pid, &uinfo->pid);
err |= __put_user(kinfo->si_uid, &uinfo->uid);
err |= __put_user(kinfo->si_status, &uinfo->status);
err |= __put_user(kinfo->si_utime, &uinfo->utime);
err |= __put_user(kinfo->si_stime, &uinfo->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->pid);
err |= __put_user(kinfo->si_uid, &uinfo->uid);
err |= __put_user((long)kinfo->si_ptr, &uinfo->svptr);
break;
default: /* this is just in case for now ... */
err |= __put_user(kinfo->si_pid, &uinfo->pid);
err |= __put_user(kinfo->si_uid, &uinfo->uid);
break;
}
return err ? -EFAULT: sizeof(*uinfo);
}
static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
int nonblock)
{
ssize_t ret;
struct signalfd_lockctx lk;
DECLARE_WAITQUEUE(wait, current);
if (!signalfd_lock(ctx, &lk))
return 0;
ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
switch (ret) {
case 0:
if (!nonblock)
break;
ret = -EAGAIN;
default:
signalfd_unlock(&lk);
return ret;
}
add_wait_queue(&ctx->wqh, &wait);
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
ret = dequeue_signal(lk.tsk, &ctx->sigmask, info);
signalfd_unlock(&lk);
if (ret != 0)
break;
if (signal_pending(current)) {
ret = -ERESTARTSYS;
break;
}
schedule();
ret = signalfd_lock(ctx, &lk);
if (unlikely(!ret)) {
/*
* Let the caller read zero byte, ala socket
* recv() when the peer disconnect. This test
* must be done before doing a dequeue_signal(),
* because if the sighand has been orphaned,
* the dequeue_signal() call is going to crash
* because ->sighand will be long gone.
*/
break;
}
}
remove_wait_queue(&ctx->wqh, &wait);
__set_current_state(TASK_RUNNING);
return ret;
}
/*
* Returns either the size of a "struct signalfd_siginfo", or zero if the
* sighand we are attached to, has been orphaned. 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,
};
/*
* Create a file descriptor that is associated with our signal
* state. We can pass it around to others if we want to, but
* it will always be _our_ signal state.
*/
asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemask)
{
int error;
sigset_t sigmask;
struct signalfd_ctx *ctx;
struct sighand_struct *sighand;
struct file *file;
struct inode *inode;
struct signalfd_lockctx lk;
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;
init_waitqueue_head(&ctx->wqh);
ctx->sigmask = sigmask;
ctx->tsk = current->group_leader;
sighand = current->sighand;
/*
* Add this fd to the list of signal listeners.
*/
spin_lock_irq(&sighand->siglock);
list_add_tail(&ctx->lnk, &sighand->signalfd_list);
spin_unlock_irq(&sighand->siglock);
/*
* When we call this, the initialization must be complete, since
* anon_inode_getfd() will install the fd.
*/
error = anon_inode_getfd(&ufd, &inode, &file, "[signalfd]",
&signalfd_fops, ctx);
if (error)
goto err_fdalloc;
} else {
file = fget(ufd);
if (!file)
return -EBADF;
ctx = file->private_data;
if (file->f_op != &signalfd_fops) {
fput(file);
return -EINVAL;
}
/*
* We need to be prepared of the fact that the sighand this fd
* is attached to, has been detched. In that case signalfd_lock()
* will return 0, and we'll just skip setting the new mask.
*/
if (signalfd_lock(ctx, &lk)) {
ctx->sigmask = sigmask;
signalfd_unlock(&lk);
}
wake_up(&ctx->wqh);
fput(file);
}
return ufd;
err_fdalloc:
signalfd_cleanup(ctx);
return error;
}