commit 3136931d10e12a9b0cf3962baaada6feac1da51b
Author: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Date:   Fri Sep 21 08:33:55 2007 +0200

    From a683d652d334a546be9175b894f42dbd8e399536 Mon Sep 17 00:00:00 2001
    Subject: [PATCH] Panic in blk_rq_map_sg() from CCISS driver
    
    New scatter/gather list chaining [sg_next()] treats 'page' member of
    struct scatterlist with low bit set [0x01] as a chain pointer to
    another struct scatterlist [array].  The CCISS driver request function
    passes an uninitialized, temporary, on-stack scatterlist array to
    blk_rq_map_sq().  sg_next() interprets random data on the stack as a
    chain pointer and eventually tries to de-reference an invalid pointer,
    resulting in:
    
    [<ffffffff8031dd70>] blk_rq_map_sg+0x70/0x170
    PGD 6090c3067 PUD 0
    Oops: 0000 [1] SMP
    last sysfs file: /block/cciss!c0d0/cciss!c0d0p1/dev
    CPU 6
    Modules linked in: ehci_hcd ohci_hcd uhci_hcd
    Pid: 1, comm: init Not tainted 2.6.23-rc6-mm1 #3
    RIP: 0010:[<ffffffff8031dd70>] [<ffffffff8031dd70>] blk_rq_map_sg+0x70/0x170
    RSP: 0018:ffff81060901f768 EFLAGS: 00010206
    RAX: 000000040b161000 RBX: ffff81060901f7d8 RCX: 000000040b162c00
    RDX: 0000000000000000 RSI: ffff81060b13a260 RDI: ffff81060b139600
    RBP: 0000000000001400 R08: 00000000fffffffe R09: 0000000000000400
    R10: 0000000000000000 R11: 000000040b163000 R12: ffff810102fe0000
    R13: 0000000000000001 R14: 0000000000000001 R15: 00001e0000000000
    FS: 00000000026108f0(0063) GS:ffff810409000b80(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
    CR2: 000000010000001e CR3: 00000006090c6000 CR4: 00000000000006e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    Process init (pid: 1, threadinfo ffff81060901e000, task ffff810409020800)
    last branch before last exception/interrupt
    from [<ffffffff8031de0a>] blk_rq_map_sg+0x10a/0x170
    to [<ffffffff8031dd70>] blk_rq_map_sg+0x70/0x170
    Stack: 000000018068ea00 ffff810102fe0000 0000000000000000 ffff810011400000
    0000000000000002 0000000000000000 ffff81040b172000 ffffffff803acd3d
    0000000000003ec1 ffff8106090d5000 ffff8106090d5000 ffff810102fe0000
    Call Trace:
    [<ffffffff803acd3d>] do_cciss_request+0x15d/0x4c0
    [<ffffffff80298968>] new_slab+0x1c8/0x270
    [<ffffffff80298ffd>] __slab_alloc+0x22d/0x470
    [<ffffffff8027327b>] mempool_alloc+0x4b/0x130
    [<ffffffff8032b21e>] cfq_set_request+0xee/0x380
    [<ffffffff8027327b>] mempool_alloc+0x4b/0x130
    [<ffffffff8031ff98>] get_request+0x168/0x360
    [<ffffffff80331b0d>] rb_insert_color+0x8d/0x110
    [<ffffffff8031cfd8>] elv_rb_add+0x58/0x60
    [<ffffffff8032a329>] cfq_add_rq_rb+0x69/0xa0
    [<ffffffff8031c1ab>] elv_merged_request+0x5b/0x60
    [<ffffffff803224fd>] __make_request+0x23d/0x650
    [<ffffffff80298ffd>] __slab_alloc+0x22d/0x470
    [<ffffffff80270000>] generic_write_checks+0x140/0x190
    [<ffffffff8031f012>] generic_make_request+0x1c2/0x3a0
    <etc>
    Kernel panic - not syncing: Attempted to kill init!
    
    This patch initializes the tmp_sg array to zeroes.  Perhaps not the ultimate
    fix, but an effective work-around.  I can now boot 23-rc6-mm1 on an HP
    Proliant x86_64 with CCISS boot disk.
    
    Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>
    
     drivers/block/cciss.c |    1 +
     1 file changed, 1 insertion(+)
    Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index 5acc6c4..559497a 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -2568,6 +2568,7 @@ static void do_cciss_request(request_queue_t *q)
 	       (int)creq->nr_sectors);
 #endif				/* CCISS_DEBUG */
 
+	memset(tmp_sg, 0, sizeof(tmp_sg));
 	seg = blk_rq_map_sg(q, creq, tmp_sg);
 
 	/* get the DMA records for the setup */