Use of /proc/sys/vm/drop_caches in RHEL 4 can cause a deadlock or high system load / system hang

Issue

• A deadlock can occur between kjournald and drop_pagecache.
• After I operated "echo 1 > /proc/sys/vm/drop_caches" on the system which uses a ext3 filesystem, I experienced a deadlock.
• High system load and or hang occurs and many threads seen in system calls related to filesystems or IO stuck waiting for a spin_lock