Re: Problems with devfs v.117 (patch)

[Richard Gooch <rgooch@xxxxxxxxxxxxxxx>]

per@xxxxxxxxxxx writes:
> I've been having problems with devfs since kernel 2.4.11 (ie. devfs
> version 117). The problem (which I can easily reproduce) occurs if I
> start X and then start a number of xterms. Then /dev becomes
> unreadable and all xterms hangs. Any further access to /dev by any
> program will produce an unkillable process. E.g. "ls /dev" will hang
> and if I switch to another vc and do "kill -9" on the ls process
> nothing happens. And as a result, I can't even do a clean shutdown
> since init, umount, etc all access /dev.

Please try the appended patch and let me know if it fixes the
problem. If not, please re-submit your bug report in full.

                                Regards,

                                        Richard....
Permanent: rgooch@xxxxxxxxxxxxx
Current:   rgooch@xxxxxxxxxxxxxxx

diff -urN linux-2.4.14-pre7/Documentation/filesystems/devfs/ChangeLog 
linux/Documentation/filesystems/devfs/ChangeLog
--- linux-2.4.14-pre7/Documentation/filesystems/devfs/ChangeLog Thu Oct 11 
00:23:24 2001
+++ linux/Documentation/filesystems/devfs/ChangeLog     Sat Nov  3 01:29:39 2001
@@ -1771,3 +1771,10 @@
 - Fixed buffer underrun in <try_modload>
 
 - Moved down_read() from <search_for_entry_in_dir> to <find_entry>
+===============================================================================
+Changes for patch v196
+
+- Fixed race in <devfsd_ioctl> when setting event mask
+  Thanks to Kari Hurtta <hurtta@xxxxxxxxxxxxxxx>
+
+- Avoid deadlock in <devfs_follow_link> by using temporary buffer
diff -urN linux-2.4.14-pre7/fs/devfs/base.c linux/fs/devfs/base.c
--- linux-2.4.14-pre7/fs/devfs/base.c   Thu Oct 11 00:23:24 2001
+++ linux/fs/devfs/base.c       Sat Nov  3 01:40:10 2001
@@ -555,6 +555,11 @@
               Fixed buffer underrun in <try_modload>.
               Moved down_read() from <search_for_entry_in_dir> to <find_entry>
   v0.119
+    20011029   Richard Gooch <rgooch@xxxxxxxxxxxxx>
+              Fixed race in <devfsd_ioctl> when setting event mask.
+    20011103   Richard Gooch <rgooch@xxxxxxxxxxxxx>
+              Avoid deadlock in <devfs_follow_link> by using temporary buffer.
+  v0.120
 */
 #include <linux/types.h>
 #include <linux/errno.h>
@@ -587,7 +592,7 @@
 #include <asm/bitops.h>
 #include <asm/atomic.h>
 
-#define DEVFS_VERSION            "0.119 (20011009)"
+#define DEVFS_VERSION            "0.120 (20011103)"
 
 #define DEVFS_NAME "devfs"
 
@@ -3029,13 +3034,25 @@
 {
     int err;
     struct devfs_entry *de;
+    char *copy;
 
     de = get_devfs_entry_from_vfs_inode (dentry->d_inode, TRUE);
     if (!de) return -ENODEV;
     down_read (&symlink_rwsem);
-    err = de->registered ? vfs_follow_link (nd,
-                                           de->u.symlink.linkname) : -ENODEV;
+    if (!de->registered)
+    {
+       up_read (&symlink_rwsem);
+       return -ENODEV;
+    }
+    copy = kmalloc (de->u.symlink.length + 1, GFP_KERNEL);
+    if (copy) memcpy (copy, de->u.symlink.linkname, de->u.symlink.length + 1);
     up_read (&symlink_rwsem);
+    if (copy)
+    {
+       err = vfs_follow_link (nd, copy);
+       kfree (copy);
+    }
+    else err = -ENOMEM;
     return err;
 }   /*  End Function devfs_follow_link  */
 
@@ -3212,7 +3229,6 @@
 {
     int ival;
     struct fs_info *fs_info = inode->i_sb->u.generic_sbp;
-    static spinlock_t lock = SPIN_LOCK_UNLOCKED;
 
     switch (cmd)
     {
@@ -3226,7 +3242,14 @@
            doesn't matter who gets in first, as long as only one gets it  */
        if (fs_info->devfsd_task == NULL)
        {
+           static spinlock_t lock = SPIN_LOCK_UNLOCKED;
+
            if ( !spin_trylock (&lock) ) return -EBUSY;
+           if (fs_info->devfsd_task != NULL)
+           {   /*  We lost the race...  */
+               spin_unlock (&lock);
+               return -EBUSY;
+           }
            fs_info->devfsd_task = current;
            spin_unlock (&lock);
            fs_info->devfsd_file = file;