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SubjectAgain, kernel BUG at /usr/src/linux/include/linux/nfs_fs.h:167! 2.4.0-prerelease
Hi Neil,

I thought I'd seen this same bug on 2.4.0-test12 after I applied your patch
but didn't follow up until now. sorry.

Anyway, with 2.4.0-prerelease and an updated loop.c.patch, below the ksymoops
output (your patch updated to 2.4.0-prerelease), I got the following BUG reports.

So it appears as if the "obviously correct patch ;-)" doesn't fix this particular
problem, but doesn't seem to break anything obvious.

Later,
Martin

ksymoops 2.3.5 on i686 2.4.0-prerelease. Options used
-V (default)
-k /proc/ksyms (default)
-l /proc/modules (default)
-o /lib/modules/2.4.0-prerelease/ (default)
-m /boot/System.map-2.4.0-prerelease (specified)

activating NMI Watchdog ... done.
cpu: 0, clocks: 680100, slice: 226700
cpu: 1, clocks: 680100, slice: 226700
kernel BUG at /usr/src/linux/include/linux/nfs_fs.h:167!
invalid operand: 0000
CPU: 0
EIP: 0010:[<c015cf61>]
Using defaults from ksymoops -t elf32-i386 -a i386
EFLAGS: 00010286
eax: 00000039 ebx: c9183e80 ecx: 00000000 edx: 00000002
esi: cb17dcc0 edi: cb1d3d40 ebp: c962e000 esp: c962fd04
ds: 0018 es: 0018 ss: 0018
Process find (pid: 29692, stackpage=c962f000)
Stack: c022fea5 c0230040 000000a7 cabe30c0 c89c9860 00000000 c12c8294 c015bf1d
cabe30c0 c89c9860 c12c8294 00000000 00001000 c89c9860 ffffffff c12c8294
cabe30c0 fffffff4 c015c721 cabe30c0 c89c9860 c12c8294 cabe30c0 c12c8294
Call Trace: [<c022fea5>] [<c0230040>] [<c015bf1d>] [<c015c721>] [<c0125bf7>] [<c018b15c>] [<c018b064>]
[<c018b48b>] [<c0181b6f>] [<c0181d03>] [<c0181d6b>] [<c0181ef7>] [<c0152bea>] [<c0151295>] [<c0112e28>]
[<c0123ff4>] [<c014133c>] [<c014170c>] [<c0141867>] [<c014170c>] [<c0123548>] [<c0108fd3>]
Code: 0f 0b 83 c4 0c 89 7e 1c eb 26 90 8d 74 26 00 6a 00 8b 54 24

>>EIP; c015cf61 <nfs_create_request+195/1e4> <=====
Trace; c022fea5 <devfsd_buf_size+1b85/10a8c>
Trace; c0230040 <devfsd_buf_size+1d20/10a8c>
Trace; c015bf1d <nfs_readpage_async+13d/1c0>
Trace; c015c721 <nfs_readpage+c5/12c>
Trace; c0125bf7 <do_generic_file_read+347/53c>
Trace; c018b15c <lo_receive+58/68>
Trace; c018b064 <lo_read_actor+0/a0>
Trace; c018b48b <do_lo_request+31f/414>
Trace; c0181b6f <__make_request+5bb/638>
Trace; c0181d03 <generic_make_request+117/124>
Trace; c0181d6b <submit_bh+5b/7c>
Trace; c0181ef7 <ll_rw_block+127/188>
Trace; c0152bea <ext2_bread+ce/110>
Trace; c0151295 <ext2_readdir+91/37c>
Trace; c0112e28 <do_page_fault+0/3e8>
Trace; c0123ff4 <do_munmap+58/250>
Trace; c014133c <vfs_readdir+8c/e8>
Trace; c014170c <filldir64+0/10c>
Trace; c0141867 <sys_getdents64+4f/b8>
Trace; c014170c <filldir64+0/10c>
Trace; c0123548 <sys_brk+b4/d8>
Trace; c0108fd3 <system_call+33/38>
Code; c015cf61 <nfs_create_request+195/1e4>
00000000 <_EIP>:
Code; c015cf61 <nfs_create_request+195/1e4> <=====
0: 0f 0b ud2a <=====
Code; c015cf63 <nfs_create_request+197/1e4>
2: 83 c4 0c add $0xc,%esp
Code; c015cf66 <nfs_create_request+19a/1e4>
5: 89 7e 1c mov %edi,0x1c(%esi)
Code; c015cf69 <nfs_create_request+19d/1e4>
8: eb 26 jmp 30 <_EIP+0x30> c015cf91 <nfs_create_request+1c5/1e4>
Code; c015cf6b <nfs_create_request+19f/1e4>
a: 90 nop
Code; c015cf6c <nfs_create_request+1a0/1e4>
b: 8d 74 26 00 lea 0x0(%esi,1),%esi
Code; c015cf70 <nfs_create_request+1a4/1e4>
f: 6a 00 push $0x0
Code; c015cf72 <nfs_create_request+1a6/1e4>
11: 8b 54 24 00 mov 0x0(%esp,1),%edx

kernel BUG at /usr/src/linux/include/linux/nfs_fs.h:167!
invalid operand: 0000
CPU: 1
EIP: 0010:[<c015cf61>]
EFLAGS: 00010286
eax: 00000039 ebx: c9183e80 ecx: 00000000 edx: 01000000
esi: c87c3ce0 edi: cb1d3d40 ebp: c5f38000 esp: c5f39d2c
ds: 0018 es: 0018 ss: 0018
Process find (pid: 29930, stackpage=c5f39000)
Stack: c022fea5 c0230040 000000a7 cabe3360 c8ad1040 00000000 c115d0d4 c015bf1d
cabe3360 c8ad1040 c115d0d4 00000000 00001000 c8ad1040 ffffffff c115d0d4
cabe3360 fffffff4 c015c721 cabe3360 c8ad1040 c115d0d4 cabe3360 c115d0d4
Call Trace: [<c022fea5>] [<c0230040>] [<c015bf1d>] [<c015c721>] [<c0125bf7>] [<c018b15c>] [<c018b064>]
[<c018b48b>] [<c0181b6f>] [<c0181d03>] [<c0181d6b>] [<c0181ef7>] [<c0151347>] [<c0112e28>] [<c0123ff4>]
[<c014133c>] [<c014170c>] [<c0141867>] [<c014170c>] [<c0123548>] [<c0108fd3>]
Code: 0f 0b 83 c4 0c 89 7e 1c eb 26 90 8d 74 26 00 6a 00 8b 54 24

>>EIP; c015cf61 <nfs_create_request+195/1e4> <=====
Trace; c022fea5 <devfsd_buf_size+1b85/10a8c>
Trace; c0230040 <devfsd_buf_size+1d20/10a8c>
Trace; c015bf1d <nfs_readpage_async+13d/1c0>
Trace; c015c721 <nfs_readpage+c5/12c>
Trace; c0125bf7 <do_generic_file_read+347/53c>
Trace; c018b15c <lo_receive+58/68>
Trace; c018b064 <lo_read_actor+0/a0>
Trace; c018b48b <do_lo_request+31f/414>
Trace; c0181b6f <__make_request+5bb/638>
Trace; c0181d03 <generic_make_request+117/124>
Trace; c0181d6b <submit_bh+5b/7c>
Trace; c0181ef7 <ll_rw_block+127/188>
Trace; c0151347 <ext2_readdir+143/37c>
Trace; c0112e28 <do_page_fault+0/3e8>
Trace; c0123ff4 <do_munmap+58/250>
Trace; c014133c <vfs_readdir+8c/e8>
Trace; c014170c <filldir64+0/10c>
Trace; c0141867 <sys_getdents64+4f/b8>
Trace; c014170c <filldir64+0/10c>
Trace; c0123548 <sys_brk+b4/d8>
Trace; c0108fd3 <system_call+33/38>
Code; c015cf61 <nfs_create_request+195/1e4>
00000000 <_EIP>:
Code; c015cf61 <nfs_create_request+195/1e4> <=====
0: 0f 0b ud2a <=====
Code; c015cf63 <nfs_create_request+197/1e4>
2: 83 c4 0c add $0xc,%esp
Code; c015cf66 <nfs_create_request+19a/1e4>
5: 89 7e 1c mov %edi,0x1c(%esi)
Code; c015cf69 <nfs_create_request+19d/1e4>
8: eb 26 jmp 30 <_EIP+0x30> c015cf91 <nfs_create_request+1c5/1e4>
Code; c015cf6b <nfs_create_request+19f/1e4>
a: 90 nop
Code; c015cf6c <nfs_create_request+1a0/1e4>
b: 8d 74 26 00 lea 0x0(%esi,1),%esi
Code; c015cf70 <nfs_create_request+1a4/1e4>
f: 6a 00 push $0x0
Code; c015cf72 <nfs_create_request+1a6/1e4>
11: 8b 54 24 00 mov 0x0(%esp,1),%edx


updated patch for 2.4.0-prerelease
__________________________________

--- loop.c.orig Fri Dec 29 16:07:21 2000
+++ loop.c Tue Jan 2 17:11:38 2001
@@ -441,37 +441,18 @@
if (!aops->prepare_write || !aops->commit_write)
lo->lo_flags |= LO_FLAGS_READ_ONLY;

- error = get_write_access(inode);
- if (error)
- goto out_putf;

/* Backed by a regular file - we need to hold onto a file
- structure for this file. Friggin' NFS can't live without
- it on write and for reading we use do_generic_file_read(),
- so... We create a new file structure based on the one
- passed to us via 'arg'. This is to avoid changing the file
- structure that the caller is using */
+ structure for this file. There is no reliable way to
+ copy it (due to a filesys private field that may be ref-count
ed)
+ so we just keep the reference to the file like a "dup" would.
+ */

lo->lo_device = inode->i_dev;
lo->lo_flags |= LO_FLAGS_DO_BMAP;

- error = -ENFILE;
- lo->lo_backing_file = get_empty_filp();
- if (lo->lo_backing_file == NULL) {
- put_write_access(inode);
- goto out_putf;
- }
-
- lo->lo_backing_file->f_mode = file->f_mode;
- lo->lo_backing_file->f_pos = file->f_pos;
- lo->lo_backing_file->f_flags = file->f_flags;
- lo->lo_backing_file->f_owner = file->f_owner;
- lo->lo_backing_file->f_dentry = file->f_dentry;
- lo->lo_backing_file->f_vfsmnt = mntget(file->f_vfsmnt);
- lo->lo_backing_file->f_op = fops_get(file->f_op);
- lo->lo_backing_file->private_data = file->private_data;
- file_moveto(lo->lo_backing_file, file);
-
+ lo->lo_backing_file = file;
+ get_file(file);
error = 0;
}

@@ -539,8 +520,6 @@

if (lo->lo_backing_file != NULL) {
struct file *filp = lo->lo_backing_file;
- if ((filp->f_mode & FMODE_WRITE) == 0)
- put_write_access(filp->f_dentry->d_inode);
fput(filp);
lo->lo_backing_file = NULL;
} else {
--------------------------------------------------------------------------------------------
Neil Brown wrote:
> On Monday December 18, trond.myklebust@fys.uio.no wrote:
> > >>>>> " " == M H VanLeeuwen <vanl@megsinet.net> writes:
> >
> > > Trond, Neil I don't know if this is a loopback bug or an NFS
> > > bug but since nfs_fs.h was implicated so I thought one of you
> > > may be interested.
> >
> > > Could you let me know if you know this problem has already been
> > > fixed or if you need more info.
> >
> > Hi,
> >
> > As far as I'm concerned, it's a loopback bug.
>
> I read it the same way.
> Actually, I cannot see the point of copying the "struct file"! Why
> not just take a reference to it? The comment tries to justify it, but
> I don't buy it.
>
> Would you mind trying the following patch (totally untested, but
> obviously correct :-)
>
> NeilBrown
>
> --- drivers/block/loop.c 2000/12/18 10:25:22 1.1
> +++ drivers/block/loop.c 2000/12/18 11:23:52
> @@ -441,37 +441,18 @@
> if (!aops->prepare_write || !aops->commit_write)
> lo->lo_flags |= LO_FLAGS_READ_ONLY;
>
> - error = get_write_access(inode);
> - if (error)
> - goto out_putf;
>
> /* Backed by a regular file - we need to hold onto a file
> - structure for this file. Friggin' NFS can't live without
> - it on write and for reading we use do_generic_file_read(),
> - so... We create a new file structure based on the one
> - passed to us via 'arg'. This is to avoid changing the file
> - structure that the caller is using */
> + structure for this file. There is no reliable way to
> + copy it (due to a filesys private field that may be ref-counted)
> + so we just keep a reference to the file like a "dup" would.
> + */
>
> lo->lo_device = inode->i_dev;
> lo->lo_flags = LO_FLAGS_DO_BMAP;
>
> - error = -ENFILE;
> - lo->lo_backing_file = get_empty_filp();
> - if (lo->lo_backing_file == NULL) {
> - put_write_access(inode);
> - goto out_putf;
> - }
> -
> - lo->lo_backing_file->f_mode = file->f_mode;
> - lo->lo_backing_file->f_pos = file->f_pos;
> - lo->lo_backing_file->f_flags = file->f_flags;
> - lo->lo_backing_file->f_owner = file->f_owner;
> - lo->lo_backing_file->f_dentry = file->f_dentry;
> - lo->lo_backing_file->f_vfsmnt = mntget(file->f_vfsmnt);
> - lo->lo_backing_file->f_op = fops_get(file->f_op);
> - lo->lo_backing_file->private_data = file->private_data;
> - file_moveto(lo->lo_backing_file, file);
> -
> + lo->lo_backing_file = file;
> + get_file(file);
> error = 0;
> }
>
> @@ -539,8 +520,6 @@
>
> if (lo->lo_backing_file != NULL) {
> struct file *filp = lo->lo_backing_file;
> - if ((filp->f_mode & FMODE_WRITE) == 0)
> - put_write_access(filp->f_dentry->d_inode);
> fput(filp);
> lo->lo_backing_file = NULL;
> } else {
>
> >
> > Somebody appears to be trying to copy a 'struct file' in the routine
> > 'loop_set_fd'. This will cause havoc in any and all filesystems that
> > rely on f_ops->open() , f_ops->release() to maintain internal data.
> > In this case, it's the file's RPC authorizations, that are getting
> > garbage-collected from beneath you once the original struct file gets
> > fput() at the end of the routine.
> >
> > Cheers,
> > Trond
-
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