CVS commit: src/sys/ufs/ufs

["Emmanuel Dreyfus" <manu%netbsd.org@localhost>]

Module Name:    src
Committed By:   manu
Date:           Sat Nov 15 05:03:55 UTC 2014

Modified Files:
        src/sys/ufs/ufs: ufs_extattr.c

Log Message:
Fix UFS1 extended attribute backend autocreation deadlock

UFS1 extended attribute backend autocration goes through a vn_open()
to create the backend file, and this forces us to release the lock
on the target node, in case the target is within the parents of the
backend file. That created a window within which another thread could
acquire a lock on the target vnode and deadlock awaiting for the
mount extended attribute lock.

We fix the problem by also releasing the mount extended attribute lock
when calling vn_open(), but that lets another thread race us for backend
creation. We just detect this using O_EXCL for vn_open() and by checking
for EEXIST return code. If we are raced, we fail backend creation but
this is not a problem since another thread succeeded on it: we just have
to use the result.


To generate a diff of this commit:
cvs rdiff -u -r1.44 -r1.45 src/sys/ufs/ufs/ufs_extattr.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.