6aba400a70
If a selinfo object is recorded (via selrecord()) and then it is quickly destroyed, with the waiters missing the opportunity to awake, at the next iteration they will find the selinfo object destroyed, causing a PF#. That happens because the selinfo interface has no way to drain the waiters before to destroy the registered selinfo object. Also this race is quite rare to get in practice, because it would require a selrecord(), a poll request by another thread and a quick destruction of the selrecord()'ed selinfo object. Fix this by adding the seldrain() routine which should be called before to destroy the selinfo objects (in order to avoid such case), and fix the present cases where it might have already been called. Sometimes, the context is safe enough to prevent this type of race, like it happens in device drivers which installs selinfo objects on poll callbacks. There, the destruction of the selinfo object happens at driver detach time, when all the filedescriptors should be already closed, thus there cannot be a race. For this case, mfi(4) device driver can be set as an example, as it implements a full correct logic for preventing this from happening. Sponsored by: Sandvine Incorporated Reported by: rstone Tested by: pluknet Reviewed by: jhb, kib Approved by: re (bz) MFC after: 3 weeks
62 lines
2.4 KiB
C
62 lines
2.4 KiB
C
/*-
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* Copyright (c) 1992, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)select.h 8.2 (Berkeley) 1/4/94
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* $FreeBSD$
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*/
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#ifndef _SYS_SELINFO_H_
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#define _SYS_SELINFO_H_
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#include <sys/event.h> /* for struct klist */
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struct selfd;
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TAILQ_HEAD(selfdlist, selfd);
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/*
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* Used to maintain information about processes that wish to be
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* notified when I/O becomes possible.
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*/
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struct selinfo {
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struct selfdlist si_tdlist; /* List of sleeping threads. */
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struct knlist si_note; /* kernel note list */
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struct mtx *si_mtx; /* Lock for tdlist. */
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};
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#define SEL_WAITING(si) (!TAILQ_EMPTY(&(si)->si_tdlist))
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#ifdef _KERNEL
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void seldrain(struct selinfo *sip);
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void selrecord(struct thread *selector, struct selinfo *sip);
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void selwakeup(struct selinfo *sip);
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void selwakeuppri(struct selinfo *sip, int pri);
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void seltdfini(struct thread *td);
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#endif
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#endif /* !_SYS_SELINFO_H_ */
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