Date: Thu, 28 May 2009 22:25:42 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Jaakko Heinonen <jh@saunalahti.fi> Cc: freebsd-fs@freebsd.org Subject: Re: VOP_WRITE & read-only file system Message-ID: <20090528192542.GB1927@deviant.kiev.zoral.com.ua> In-Reply-To: <20090528172943.GA3859@a91-153-125-115.elisa-laajakaista.fi> References: <20090527150258.GA3666@a91-153-125-115.elisa-laajakaista.fi> <20090527153543.GK1927@deviant.kiev.zoral.com.ua> <20090528172943.GA3859@a91-153-125-115.elisa-laajakaista.fi>
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[-- Attachment #1 --] On Thu, May 28, 2009 at 08:29:43PM +0300, Jaakko Heinonen wrote: > > Hi, > > On 2009-05-27, Kostik Belousov wrote: > > > 1) mmap(2) > > > - mmap(2) a file > > > - close(2) the file handle > > > - remount file-system as read-only > > > - modify mapped memory > > > Yes, the issue is there. Real cause for the problem is that mmap() does > > not increment v_writecnt of the vnode that backs shared writable mappings. > > > > I have a patch that fixes this, see > > http://people.freebsd.org/~kib/misc/vm_map_delete.3.patch > > The patch seems to have a problem with forced remount or unmount. After > a forced remount to read-only munmap(2) crashes in _vm_map_unlock() > due to NULL vp. > > #12 0xc08f0cb3 in _vn_lock (vp=0x0, flags=525312, > file=0xc0c55e8f "/home/jaakko/src/head/sys/vm/vm_map.c", line=494) > at vnode_if.h:830 > #13 0xc0a8cb4f in _vm_map_unlock (map=0xc634f000, process_freelist=1, > file=0xc0c56902 "/home/jaakko/src/head/sys/vm/vm_mmap.c", line=597) > at /home/jaakko/src/head/sys/vm/vm_map.c:494 > #14 0xc0a91d98 in munmap (td=0xc5a996c0, uap=0xf480ecf8) > at /home/jaakko/src/head/sys/vm/vm_mmap.c:597 > #15 0xc0b637b3 in syscall (frame=0xf480ed38) > at /home/jaakko/src/head/sys/i386/i386/trap.c:1073 > #16 0xc0b46a10 in Xint0x80_syscall () > at /home/jaakko/src/head/sys/i386/i386/exception.s:261 I expect that http://people.freebsd.org/~kib/misc/vm_map_delete.4.patch fix the issue. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkoe5TUACgkQC3+MBN1Mb4g6DQCeOBxmZ/zOeCtzdoApYGyTcSmM /N4AoLAfi4Sf1+CUZ7zDgLsaG2DvzNzC =MMtG -----END PGP SIGNATURE-----
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