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![Eric W. Biederman](/assets/img/avatar_default.png)
Linus recently observed that if we did not worry about the padding member in struct siginfo it is only about 48 bytes, and 48 bytes is much nicer than 128 bytes for allocating on the stack and copying around in the kernel. The obvious thing of only adding the padding when userspace is including siginfo.h won't work as there are sigframe definitions in the kernel that embed struct siginfo. So split siginfo in two; kernel_siginfo and siginfo. Keeping the traditional name for the userspace definition. While the version that is used internally to the kernel and ultimately will not be padded to 128 bytes is called kernel_siginfo. The definition of struct kernel_siginfo I have put in include/signal_types.h A set of buildtime checks has been added to verify the two structures have the same field offsets. To make it easy to verify the change kernel_siginfo retains the same size as siginfo. The reduction in size comes in a following change. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
361 lines
9 KiB
C
361 lines
9 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* fs/signalfd.c
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*
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* Copyright (C) 2003 Linus Torvalds
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*
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* Mon Mar 5, 2007: Davide Libenzi <davidel@xmailserver.org>
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* Changed ->read() to return a siginfo strcture instead of signal number.
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* Fixed locking in ->poll().
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* Added sighand-detach notification.
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* Added fd re-use in sys_signalfd() syscall.
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* Now using anonymous inode source.
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* Thanks to Oleg Nesterov for useful code review and suggestions.
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* More comments and suggestions from Arnd Bergmann.
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* Sat May 19, 2007: Davi E. M. Arnaut <davi@haxent.com.br>
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* Retrieve multiple signals with one read() call
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* Sun Jul 15, 2007: Davide Libenzi <davidel@xmailserver.org>
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* Attach to the sighand only during read() and poll().
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*/
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#include <linux/file.h>
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#include <linux/poll.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/kernel.h>
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#include <linux/signal.h>
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#include <linux/list.h>
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#include <linux/anon_inodes.h>
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#include <linux/signalfd.h>
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#include <linux/syscalls.h>
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#include <linux/proc_fs.h>
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#include <linux/compat.h>
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void signalfd_cleanup(struct sighand_struct *sighand)
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{
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wait_queue_head_t *wqh = &sighand->signalfd_wqh;
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/*
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* The lockless check can race with remove_wait_queue() in progress,
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* but in this case its caller should run under rcu_read_lock() and
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* sighand_cachep is SLAB_TYPESAFE_BY_RCU, we can safely return.
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*/
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if (likely(!waitqueue_active(wqh)))
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return;
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/* wait_queue_entry_t->func(POLLFREE) should do remove_wait_queue() */
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wake_up_poll(wqh, EPOLLHUP | POLLFREE);
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}
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struct signalfd_ctx {
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sigset_t sigmask;
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};
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static int signalfd_release(struct inode *inode, struct file *file)
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{
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kfree(file->private_data);
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return 0;
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}
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static __poll_t signalfd_poll(struct file *file, poll_table *wait)
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{
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struct signalfd_ctx *ctx = file->private_data;
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__poll_t events = 0;
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poll_wait(file, ¤t->sighand->signalfd_wqh, wait);
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spin_lock_irq(¤t->sighand->siglock);
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if (next_signal(¤t->pending, &ctx->sigmask) ||
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next_signal(¤t->signal->shared_pending,
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&ctx->sigmask))
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events |= EPOLLIN;
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spin_unlock_irq(¤t->sighand->siglock);
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return events;
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}
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/*
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* Copied from copy_siginfo_to_user() in kernel/signal.c
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*/
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static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
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kernel_siginfo_t const *kinfo)
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{
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struct signalfd_siginfo new;
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BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
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/*
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* Unused members should be zero ...
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*/
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memset(&new, 0, sizeof(new));
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/*
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* If you change siginfo_t structure, please be sure
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* this code is fixed accordingly.
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*/
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new.ssi_signo = kinfo->si_signo;
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new.ssi_errno = kinfo->si_errno;
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new.ssi_code = kinfo->si_code;
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switch (siginfo_layout(kinfo->si_signo, kinfo->si_code)) {
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case SIL_KILL:
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new.ssi_pid = kinfo->si_pid;
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new.ssi_uid = kinfo->si_uid;
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break;
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case SIL_TIMER:
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new.ssi_tid = kinfo->si_tid;
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new.ssi_overrun = kinfo->si_overrun;
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new.ssi_ptr = (long) kinfo->si_ptr;
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new.ssi_int = kinfo->si_int;
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break;
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case SIL_POLL:
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new.ssi_band = kinfo->si_band;
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new.ssi_fd = kinfo->si_fd;
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break;
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case SIL_FAULT_BNDERR:
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case SIL_FAULT_PKUERR:
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/*
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* Fall through to the SIL_FAULT case. Both SIL_FAULT_BNDERR
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* and SIL_FAULT_PKUERR are only generated by faults that
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* deliver them synchronously to userspace. In case someone
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* injects one of these signals and signalfd catches it treat
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* it as SIL_FAULT.
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*/
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case SIL_FAULT:
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new.ssi_addr = (long) kinfo->si_addr;
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#ifdef __ARCH_SI_TRAPNO
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new.ssi_trapno = kinfo->si_trapno;
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#endif
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break;
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case SIL_FAULT_MCEERR:
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new.ssi_addr = (long) kinfo->si_addr;
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#ifdef __ARCH_SI_TRAPNO
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new.ssi_trapno = kinfo->si_trapno;
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#endif
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new.ssi_addr_lsb = (short) kinfo->si_addr_lsb;
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break;
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case SIL_CHLD:
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new.ssi_pid = kinfo->si_pid;
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new.ssi_uid = kinfo->si_uid;
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new.ssi_status = kinfo->si_status;
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new.ssi_utime = kinfo->si_utime;
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new.ssi_stime = kinfo->si_stime;
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break;
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case SIL_RT:
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/*
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* This case catches also the signals queued by sigqueue().
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*/
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new.ssi_pid = kinfo->si_pid;
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new.ssi_uid = kinfo->si_uid;
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new.ssi_ptr = (long) kinfo->si_ptr;
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new.ssi_int = kinfo->si_int;
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break;
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case SIL_SYS:
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new.ssi_call_addr = (long) kinfo->si_call_addr;
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new.ssi_syscall = kinfo->si_syscall;
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new.ssi_arch = kinfo->si_arch;
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break;
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}
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if (copy_to_user(uinfo, &new, sizeof(struct signalfd_siginfo)))
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return -EFAULT;
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return sizeof(*uinfo);
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}
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static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, kernel_siginfo_t *info,
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int nonblock)
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{
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ssize_t ret;
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DECLARE_WAITQUEUE(wait, current);
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spin_lock_irq(¤t->sighand->siglock);
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ret = dequeue_signal(current, &ctx->sigmask, info);
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switch (ret) {
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case 0:
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if (!nonblock)
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break;
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ret = -EAGAIN;
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default:
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spin_unlock_irq(¤t->sighand->siglock);
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return ret;
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}
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add_wait_queue(¤t->sighand->signalfd_wqh, &wait);
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for (;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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ret = dequeue_signal(current, &ctx->sigmask, info);
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if (ret != 0)
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break;
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if (signal_pending(current)) {
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ret = -ERESTARTSYS;
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break;
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}
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spin_unlock_irq(¤t->sighand->siglock);
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schedule();
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spin_lock_irq(¤t->sighand->siglock);
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}
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spin_unlock_irq(¤t->sighand->siglock);
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remove_wait_queue(¤t->sighand->signalfd_wqh, &wait);
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__set_current_state(TASK_RUNNING);
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return ret;
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}
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/*
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* Returns a multiple of the size of a "struct signalfd_siginfo", or a negative
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* error code. The "count" parameter must be at least the size of a
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* "struct signalfd_siginfo".
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*/
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static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
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loff_t *ppos)
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{
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struct signalfd_ctx *ctx = file->private_data;
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struct signalfd_siginfo __user *siginfo;
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int nonblock = file->f_flags & O_NONBLOCK;
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ssize_t ret, total = 0;
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kernel_siginfo_t info;
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count /= sizeof(struct signalfd_siginfo);
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if (!count)
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return -EINVAL;
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siginfo = (struct signalfd_siginfo __user *) buf;
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do {
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ret = signalfd_dequeue(ctx, &info, nonblock);
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if (unlikely(ret <= 0))
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break;
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ret = signalfd_copyinfo(siginfo, &info);
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if (ret < 0)
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break;
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siginfo++;
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total += ret;
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nonblock = 1;
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} while (--count);
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return total ? total: ret;
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}
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#ifdef CONFIG_PROC_FS
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static void signalfd_show_fdinfo(struct seq_file *m, struct file *f)
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{
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struct signalfd_ctx *ctx = f->private_data;
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sigset_t sigmask;
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sigmask = ctx->sigmask;
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signotset(&sigmask);
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render_sigset_t(m, "sigmask:\t", &sigmask);
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}
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#endif
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static const struct file_operations signalfd_fops = {
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#ifdef CONFIG_PROC_FS
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.show_fdinfo = signalfd_show_fdinfo,
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#endif
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.release = signalfd_release,
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.poll = signalfd_poll,
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.read = signalfd_read,
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.llseek = noop_llseek,
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};
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static int do_signalfd4(int ufd, sigset_t *mask, int flags)
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{
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struct signalfd_ctx *ctx;
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/* Check the SFD_* constants for consistency. */
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BUILD_BUG_ON(SFD_CLOEXEC != O_CLOEXEC);
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BUILD_BUG_ON(SFD_NONBLOCK != O_NONBLOCK);
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if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
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return -EINVAL;
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sigdelsetmask(mask, sigmask(SIGKILL) | sigmask(SIGSTOP));
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signotset(mask);
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if (ufd == -1) {
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
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if (!ctx)
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return -ENOMEM;
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ctx->sigmask = *mask;
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/*
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* When we call this, the initialization must be complete, since
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* anon_inode_getfd() will install the fd.
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*/
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ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
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O_RDWR | (flags & (O_CLOEXEC | O_NONBLOCK)));
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if (ufd < 0)
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kfree(ctx);
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} else {
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struct fd f = fdget(ufd);
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if (!f.file)
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return -EBADF;
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ctx = f.file->private_data;
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if (f.file->f_op != &signalfd_fops) {
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fdput(f);
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return -EINVAL;
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}
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spin_lock_irq(¤t->sighand->siglock);
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ctx->sigmask = *mask;
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spin_unlock_irq(¤t->sighand->siglock);
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wake_up(¤t->sighand->signalfd_wqh);
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fdput(f);
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}
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return ufd;
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}
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SYSCALL_DEFINE4(signalfd4, int, ufd, sigset_t __user *, user_mask,
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size_t, sizemask, int, flags)
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{
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sigset_t mask;
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if (sizemask != sizeof(sigset_t) ||
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copy_from_user(&mask, user_mask, sizeof(mask)))
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return -EINVAL;
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return do_signalfd4(ufd, &mask, flags);
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}
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SYSCALL_DEFINE3(signalfd, int, ufd, sigset_t __user *, user_mask,
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size_t, sizemask)
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{
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sigset_t mask;
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if (sizemask != sizeof(sigset_t) ||
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copy_from_user(&mask, user_mask, sizeof(mask)))
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return -EINVAL;
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return do_signalfd4(ufd, &mask, 0);
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}
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#ifdef CONFIG_COMPAT
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static long do_compat_signalfd4(int ufd,
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const compat_sigset_t __user *user_mask,
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compat_size_t sigsetsize, int flags)
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{
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sigset_t mask;
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if (sigsetsize != sizeof(compat_sigset_t))
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return -EINVAL;
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if (get_compat_sigset(&mask, user_mask))
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return -EFAULT;
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return do_signalfd4(ufd, &mask, flags);
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}
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COMPAT_SYSCALL_DEFINE4(signalfd4, int, ufd,
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const compat_sigset_t __user *, user_mask,
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compat_size_t, sigsetsize,
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int, flags)
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{
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return do_compat_signalfd4(ufd, user_mask, sigsetsize, flags);
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}
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COMPAT_SYSCALL_DEFINE3(signalfd, int, ufd,
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const compat_sigset_t __user *, user_mask,
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compat_size_t, sigsetsize)
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{
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return do_compat_signalfd4(ufd, user_mask, sigsetsize, 0);
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}
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#endif
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