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This solves a deadlock that can occur when read()ing into a file-mmap()

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space. When doing this, it is possible to for another process to attempt
to get an exclusive lock on the vnode and deadlock the mmap/read
combination when the uiomove() call tries to obtain a second
shared lock on the vnode. There is still a potential deadlock
situation with write()/mmap().
Submitted by: Matt Dillon <dillon@freebsd.org>
Reviewed by: Luoqi Chen <luoqi@freebsd.org>
Delimmitted by tag PRE_MATT_MMAP_LOCK and POST_MATT_MMAP_LOCK
in kern/kern_lock.c kern/kern_subr.c
This commit is contained in:
Julian Elischer 1999-03-12 03:09:29 +00:00
parent 4ef2094e45
commit beef8a367c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=44681
2 changed files with 36 additions and 7 deletions
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27
sys/kern/kern_lock.c
View File

@ -38,7 +38,7 @@
* SUCH DAMAGE.
*
* @(#)kern_lock.c 8.18 (Berkeley) 5/21/95
* $Id: kern_lock.c,v 1.22 1999/01/10 01:58:24 eivind Exp $
* $Id: kern_lock.c,v 1.23 1999/01/20 14:49:11 eivind Exp $
*/
#include "opt_lint.h"
@ -205,9 +205,30 @@ debuglockmgr(lkp, flags, interlkp, p, name, file, line)
switch (flags & LK_TYPE_MASK) {
case LK_SHARED:
/*
* If we are not the exclusive lock holder, we have to block
* while there is an exclusive lock holder or while an
* exclusive lock request or upgrade request is in progress.
*
* However, if P_DEADLKTREAT is set, we override exclusive
* lock requests or upgrade requests ( but not the exclusive
* lock itself ).
*/
if (lkp->lk_lockholder != pid) {
error = acquire(lkp, extflags,
LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE);
if (p->p_flag & P_DEADLKTREAT) {
error = acquire(
lkp,
extflags,
LK_HAVE_EXCL
);
} else {
error = acquire(
lkp,
extflags,
LK_HAVE_EXCL | LK_WANT_EXCL |
LK_WANT_UPGRADE
);
}
if (error)
break;
sharelock(lkp, 1);

16
sys/kern/kern_subr.c
View File

@ -36,7 +36,7 @@
* SUCH DAMAGE.
*
* @(#)kern_subr.c 8.3 (Berkeley) 1/21/94
* $Id: kern_subr.c,v 1.26 1999/02/22 16:57:47 bde Exp $
* $Id: kern_subr.c,v 1.27 1999/02/22 18:39:49 bde Exp $
*/
#include <sys/param.h>
@ -63,13 +63,19 @@ uiomove(cp, n, uio)
{
register struct iovec *iov;
u_int cnt;
int error;
int error = 0;
int save = 0;
KASSERT(uio->uio_rw == UIO_READ || uio->uio_rw == UIO_WRITE,
("uiomove: mode"));
KASSERT(uio->uio_segflg != UIO_USERSPACE || uio->uio_procp == curproc,
("uiomove proc"));
if (curproc) {
save = curproc->p_flag & P_DEADLKTREAT;
curproc->p_flag |= P_DEADLKTREAT;
}
while (n > 0 && uio->uio_resid) {
iov = uio->uio_iov;
cnt = iov->iov_len;
@ -92,7 +98,7 @@ uiomove(cp, n, uio)
else
error = copyin(iov->iov_base, cp, cnt);
if (error)
return (error);
break;
break;
case UIO_SYSSPACE:
@ -111,7 +117,9 @@ uiomove(cp, n, uio)
cp += cnt;
n -= cnt;
}
return (0);
if (curproc)
curproc->p_flag = (curproc->p_flag & ~P_DEADLKTREAT) | save;
return (error);
}
int