The buffer daemon cannot skip over buffers owned by locked inodes as they may be the only viable ones to flush. Thus it will now wait for an inode lock if the other alternatives will result in rollbacks (and immediate redirtying of the buffer). If only buffers with rollbacks are available, one will be flushed, but then the buffer daemon will wait briefly before proceeding. Failing to wait briefly effectively deadlocks a uniprocessor since every other process writing to that filesystem will wait for the buffer daemon to clean up which takes close enough to forever to feel like a deadlock.
The buffer daemon cannot skip over buffers owned by locked inodes as
they may be the only viable ones to flush. Thus it will now wait for
an inode lock if the other alternatives will result in rollbacks (and
immediate redirtying of the buffer). If only buffers with rollbacks
are available, one will be flushed, but then the buffer daemon will
wait briefly before proceeding. Failing to wait briefly effectively
deadlocks a uniprocessor since every other process writing to that
filesystem will wait for the buffer daemon to clean up which takes
close enough to forever to feel like a deadlock.

Reported by:	Archie Cobbs <archie@dellroad.org>
Sponsored by:   DARPA & NAI Labs.
Approved by:	re

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase