Description of problem:
Alexander Viro has reported the following serious Linux kernel issue:
fcntl_dirnotify() adds an element to inode->i_dnotify. It contains
a reference to struct file and to struct files_struct (both not contributing
to refcounts). filp_close() (called when reference to file is removed
from descriptor table) purges element with file/descriptor table in question
from ->i_dnotify. The problem is, fcntl() can race with close() from another
thread, inserting element *after* close() is finished. If that happens,
the sucker is stuck there forever, long after the struct file it refers
to had been freed/reused/etc. Actually, even having the (in-core) inode
freed and reused doesn't clean it up - "->i_dnotify is empty on allocated
inode" is guaranteed by slab constructor; freeing and reallocating won't
touch it at all, since the list must have been emptied before we'd dropped
the final reference to inode.
NOTE: Please note this issue is NOT public yet, so handle each information
===== about this one as confidential.
Public now, lifting embargo:
Fixed upstream in 184.108.40.206.
kernel-220.127.116.11-92.fc8 has been pushed to the Fedora 8 stable repository. If problems still persist, please make note of it in this bug report.
This was addressed via:
Red Hat Enterprise Linux version 3 (RHSA-2008:0211)
Red Hat Enterprise Linux version 5 (RHSA-2008:0233)
Red Hat Enterprise Linux version 4 (RHSA-2008:0237)