cluster/cmirror-kernel/src dm-cmirror-client.c ...

[jbrassow at sourceware dot org]

CVSROOT:	/cvs/cluster
Module name:	cluster
Branch: 	RHEL4
Changes by:	jbrassow@sourceware.org	2007-04-03 19:21:10

Modified files:
	cmirror-kernel/src: dm-cmirror-client.c dm-cmirror-common.h 
	                    dm-cmirror-server.c dm-cmirror-xfr.h 

Log message:
	Bug 234539: multiple streams of I/O can cause system to lock up
	
	This bug provoked an audit of the communications exchange, locking,
	and memory allocations/stack usage.
	
	Communication fixes include:
	1) Added sequence numbers to ensure that replies from the server
	correctly correspond to client requests.  It was found that if
	a client timed out waiting for a server to respond, it would send
	the request again.  However, the server may have simply been too
	busy to respond in a timely fashion.  It ends up responding to
	both the original request and the resent request - causing the
	client and server to become out-of-sync WRT log requests.
	
	Locking fixes include:
	1) A semaphore was being "up"ed twice in some cases, rendering
	the lock impotent.
	
	2) A spin lock controlling region status lists was being held
	across blocking operations - sometimes causing deadlocks.  The
	spin lock was changed to a per-log lock, and some logging
	operations were restructured to better suit the way locking
	needed to be done.  A side-effect of this fix is a 20%
	improvement in write operations.
	
	3) The log list protection lock needed to change from a spin lock
	to a semaphore to allow blocking operations.
	
	Memory allocation fixes include:
	1) Wrong flags to kmalloc could cause deadlock.  Use NOFS instead
	of KERNEL.
	
	2) Mempools needed more reserves for low memory conditions.
	
	3) Server now allocates a communication structure instead of having
	it on the stack.  This reduces the likelyhood of stack corruption.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/cluster/cmirror-kernel/src/dm-cmirror-client.c.diff?cvsroot=cluster&only_with_tag=RHEL4&r1=1.1.2.42&r2=1.1.2.43
http://sourceware.org/cgi-bin/cvsweb.cgi/cluster/cmirror-kernel/src/dm-cmirror-common.h.diff?cvsroot=cluster&only_with_tag=RHEL4&r1=1.1.2.12&r2=1.1.2.13
http://sourceware.org/cgi-bin/cvsweb.cgi/cluster/cmirror-kernel/src/dm-cmirror-server.c.diff?cvsroot=cluster&only_with_tag=RHEL4&r1=1.1.2.27&r2=1.1.2.28
http://sourceware.org/cgi-bin/cvsweb.cgi/cluster/cmirror-kernel/src/dm-cmirror-xfr.h.diff?cvsroot=cluster&only_with_tag=RHEL4&r1=1.1.2.3&r2=1.1.2.4