Patch Name: PHKL_20849

Patch Description: s700 10.20 Fix for kthread b_sema wait queue corruption

Creation Date: 00/01/19

Post Date:  00/01/24

Hardware Platforms - OS Releases:
	s700: 10.20

Products: N/A

Filesets:
	OS-Core.CORE-KRN

Automatic Reboot?: Yes

Status: General Superseded

Critical:
	Yes
	PHKL_20849: PANIC CORRUPTION

Path Name: /hp-ux_patches/s700/10.X/PHKL_20849

Symptoms:
	PHKL_20849:
	( SR: 8606114394 CR: JAGac29158 )
	Multiprocessor system paniced with the following stack
	trace:

	panic: Spinlock deadlock!

	panic+0x3c
	too_much_time+0x238
	wait_for_lock_spinner+0x2f4
	wait_for_lock_4way+0x2c
	b_psema_retry+0x1c
	soo_select+0x44
	selscan+0x1bc
	select+0x6ec
	syscall+0x1a4
	$syscallrtn

	The panicing processor timed out waiting on a spinlock.
	The processor holding the spinlock was in a loop
	searching for a thread that wanted the beta semaphore
	the panicing processor was releasing. The kt_wait_list
	chain was corrupted.

	The trace for the looping processor showed:

	crash event was a TOC

	b_sema_get_queue+0x2c
	mp_b_sema_wanted+0x38
	sounlock+0x3f4
	mp_socket_unlock+0x10
	soclose+0x128
	soo_close+0x7c
	closef+0x6c
	close+0x40
	syscall+0x64c
	$syscallrtn+0x0

Defect Description:
	PHKL_20849:
	( SR: 8606114394 CR: JAGac29158 )
	mp_b_sema_wanted() is called to check if there is a
	kthread at the head of the semaphore's wait queue
	that needs to be awaken when the semaphore is
	available. In acquiring the thread lock, this
	routine momentarily releases the spinlock associated
	with the semaphore and it assumes that the list of
	waiters for this lock has not changed. If the wait
	list for the semaphore lock was changed during
	the window, mp_b_sema_wanted() passes the semaphore
	lock to the wrong kthread and corrupts the kt_wait_list.

	Resolution:
	Added a check and retry to ensure the kt_wait queue
	was not changed after reacquiring the semaphore spinlock.

SR:
	8606114394

Patch Files:
	/usr/conf/lib/libhp-ux.a(sem_beta.o)

what(1) Output:
	/usr/conf/lib/libhp-ux.a(sem_beta.o):
		sem_beta.c    $Date: 2000/01/18 10:49:52 $ $Revision
			: 1.12.98.6 $ PATCH_10.20 (PHKL_20849)

cksum(1) Output:
	4160049012 4820 /usr/conf/lib/libhp-ux.a(sem_beta.o)

Patch Conflicts: None

Patch Dependencies: None

Hardware Dependencies: None

Other Dependencies: None

Supersedes: None

Equivalent Patches:
	PHKL_20850:
	s800: 10.20

	PHKL_20851:
	s700: 11.00

Patch Package Size: 60 KBytes

Installation Instructions:
	Please review all instructions and the Hewlett-Packard
	SupportLine User Guide or your Hewlett-Packard support terms
	and conditions for precautions, scope of license,
	restrictions, and, limitation of liability and warranties,
	before installing this patch.
	------------------------------------------------------------
	1. Back up your system before installing a patch.

	2. Login as root.

	3. Copy the patch to the /tmp directory.

	4. Move to the /tmp directory and unshar the patch:

		cd /tmp
		sh PHKL_20849

	5a. For a standalone system, run swinstall to install the
	    patch:

		swinstall -x autoreboot=true -x match_target=true \
			-s /tmp/PHKL_20849.depot

	By default swinstall will archive the original software in
	/var/adm/sw/patch/PHKL_20849.  If you do not wish to retain a
	copy of the original software, you can create an empty file
	named /var/adm/sw/patch/PATCH_NOSAVE.

	WARNING: If this file exists when a patch is installed, the
	         patch cannot be deinstalled.  Please be careful
		 when using this feature.

	It is recommended that you move the PHKL_20849.text file to
	/var/adm/sw/patch for future reference.

	To put this patch on a magnetic tape and install from the
	tape drive, use the command:

		dd if=/tmp/PHKL_20849.depot of=/dev/rmt/0m bs=2k

Special Installation Instructions: None