Date: Thu, 28 May 2009 20:29:43 +0300 From: Jaakko Heinonen <jh@saunalahti.fi> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: VOP_WRITE & read-only file system Message-ID: <20090528172943.GA3859@a91-153-125-115.elisa-laajakaista.fi> In-Reply-To: <20090527153543.GK1927@deviant.kiev.zoral.com.ua> References: <20090527150258.GA3666@a91-153-125-115.elisa-laajakaista.fi> <20090527153543.GK1927@deviant.kiev.zoral.com.ua>
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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 > During remount rw->ro or unmount, UFS filesystem is suspended, see > r183074. Thanks for the pointer. -- Jaakko
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