[uml-devel] [PATCH] fix for: Host panic when UML reads host /dev/shm

[uml-devel] [PATCH] fix for: Host panic when UML reads host /dev/shm

[James W McMechan]

Ok here are the two patches one each for 2.4.23
and 2.6.0-test11
Linus has accepted the test11 patch into bk so
the next 2.6 kernel should have the fix
I have also been testing a 2.4.23 patch
They no longer oopes with any of my test programs
Since you were having problems here they are

Enjoy, James McMechan

The problem was that the list_del was deleting
the cursor while the p pointer was at the cursor
the list_add_tail then oopes on the poisoned
pointers, since the cursor was to be deleted
anyway and should not be counted as a entry
it could be deleted earlier so p never points
to it, and then list_add_tail doesn't hit the
poisoned pointers in the cursor entry.
Of course the simple solution was after about
six much uglier patches that also fixed the
problem in other ways.

diff -Nur linux-2.6.0-test11/fs/libfs.c build-2.6.0-test11-bug/fs/libfs.c
      
--- linux-2.6.0-test11/fs/libfs.c       2003-11-26 12:42:48.000000000
-0800
+++ build-2.6.0-test11-bug/fs/libfs.c   2003-12-07 13:07:19.000000000
-0800
@@ -79,6 +79,7 @@
                        loff_t n = file->f_pos - 2;
                                                                         
      
                        spin_lock(&dcache_lock);                         
      
+                       list_del(&cursor->d_child);                      
      
                        p = file->f_dentry->d_subdirs.next;
                        while (n && p != &file->f_dentry->d_subdirs) {
                                struct dentry *next;
@@ -87,7 +88,6 @@                                                        
      
                                        n--;                             
      
                                p = p->next;                             
      
                        }                                                
      
-                       list_del(&cursor->d_child);                      
      
                        list_add_tail(&cursor->d_child, p);
                        spin_unlock(&dcache_lock);
                }

diff -Nur linux-2.4.23/fs/readdir.c build-2.4.23-skas/fs/readdir.c
--- linux-2.4.23/fs/readdir.c   2002-08-02 17:39:45.000000000 -0700
+++ build-2.4.23-skas/fs/readdir.c      2003-12-10 06:01:05.000000000
-0800
@@ -69,6 +69,7 @@
                        loff_t n = file->f_pos - 2;

                        spin_lock(&dcache_lock);
+                       list_del(&cursor->d_child);
                        p = file->f_dentry->d_subdirs.next;
                        while (n && p != &file->f_dentry->d_subdirs) {
                                struct dentry *next;
@@ -77,7 +78,6 @@
                                        n--;
                                p = p->next;
                        }
-                       list_del(&cursor->d_child);
                        list_add_tail(&cursor->d_child, p);
                        spin_unlock(&dcache_lock);
                }

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Re: [uml-devel] [PATCH] fix for: Host panic when UML reads host /dev/shm

[BlaisorBlade]

Alle 16:36, mercoledì 10 dicembre 2003, James W McMechan ha scritto:
> Ok here are the two patches one each for 2.4.23
> and 2.6.0-test11
> Linus has accepted the test11 patch into bk so
> the next 2.6 kernel should have the fix
> I have also been testing a 2.4.23 patch
> They no longer oopes with any of my test programs
> Since you were having problems here they are
Compliments for the catch! I had been trying uselessly to find the bug inside 
the shm code(I had found that which was the invalid pointer, but nothing 
after that)...

Are you going to send that for 2.4.24? That one will be the last 2.4 kernel...
In the meantime, I think that people at http://www.hardrock.org/ will be happy 
of it... it's the -uv tree(not very famous, maybe, but even kerneltrap.org 
speaks about it).

By the way: if this is the problem, then why didn't the kernel oops on /proc 
reads? Isn't it a memory based fs, too?

-- 
cat <<EOSIGN
Paolo Giarrusso, aka Blaisorblade
Linux Kernel 2.4.21/2.6.0-test on an i686; Linux registered user n. 292729
EOSIGN



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