Messages in this thread Patch in this message | | | Date | Tue, 29 Apr 2008 00:22:33 +0200 | From | Henry Nestler <> | Subject | Re: [PATCH] x86: endless page faults in mount_block_root for Linux 2.6 |
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Prevents side effects from non vmalloc and non userspace page faults for sys_mount of root filesystem with automatic fs_type detection.
do_mount_root should call with page alignment buffer. The underlaying sys_mount does copy 4096 bytes from given parameter with function exact_copy_from_user, and the page after "fs_names+4096" can be mapped or not. The fault handler can never map it, address is not from vmalloc.
Signed-off-by: Henry Nestler <henry.ne@arcor.de> ---
Ingo Molnar wrote: > * Henry Nestler <Henry.Ne@Arcor.de> wrote: > >> An other fix would be to copy the "fs_names+offset" into a new page >> and give a page alignment buffer to do_mount_root. I feel it is better >> to fix the fault handler for all failed addresses, not only the mount? > > agreed - but this would be a VFS fix, Al Cc:-ed. I ran into that > property of the mount string copy myself in the past.
The patch is a nice to have, if the fault handler works properly.
I'm not shure with the VFS fix. The change only has effect for x86 and x86_64. I'm afraid. Mostly other architectures no need to change. I would only public the base of the problem. Perhaps no need to change here.
> (note, your patches were whitespace damaged - i fixed up the x86 fix by > hand - you might want to resend the VFS one via > Documentation/email-clients.txt.)
Sorry, was wrong copy&paste.
=================================== diff --git a/init/do_mounts.c b/init/do_mounts.c index 3885e70..c730511 100644 --- a/init/do_mounts.c +++ b/init/do_mounts.c @@ -204,6 +204,7 @@ static int __init do_mount_root(char *name, char *fs, int flags, void *data) void __init mount_block_root(char *name, int flags) { char *fs_names = __getname(); + char *fs_type = __getname(); char *p; #ifdef CONFIG_BLOCK char b[BDEVNAME_SIZE]; @@ -214,7 +215,12 @@ void __init mount_block_root(char *name, int flags) get_fs_names(fs_names); retry: for (p = fs_names; *p; p += strlen(p)+1) { - int err = do_mount_root(name, p, flags, root_mount_data); + int err; + + /* fs_type must size >= PAGE_SIZE or in user space */ + strcpy(fs_type, p); + + err = do_mount_root(name, fs_type, flags, root_mount_data); switch (err) { case 0: goto out; @@ -251,6 +257,7 @@ retry: #endif panic("VFS: Unable to mount root fs on %s", b); out: + putname(fs_type); putname(fs_names); }
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