blkparse: Fix a potential coredump issue

blkparse: Fix a potential coredump issue

Executing "blkparse -t" may cause coredump due to
accessing uninitialized memory.

8,16   0     6092     1.436280373 20685  Q   W 15356912 + 4096 [kworker/u256:2]
8,16   0     6093     1.436282093 20685  X   W 15356912 / 15357936 [kworker/u256:2]
8,16   0     6094     1.436282735 20685  G   W 15356912 + 1024 [kworker/u256:2]
8,16   0     6099     1.436358617 20685  X   W 15357936 / 15358960 [kworker/u256:2]
8,16   0     6100     1.436359418 20685  G   W 15357936 + 1024 [kworker/u256:2]
8,16   0     6102     1.436359931 20685  I   W 15356912 + 1024 [kworker/u256:2]
8,16   0     6103     1.436360874 20685  D   W 15356912 + 1024 [kworker/u256:2]
8,16   0     6105     1.436436572 20685  X   W 15358960 / 15359984 [kworker/u256:2]
8,16   0     6106     1.436437679 20685  G   W 15358960 + 1024 [kworker/u256:2]
8,16   0     6108     1.436438205 20685  I   W 15357936 + 1024 [kworker/u256:2]
8,16   0     6109     1.436439368 20685  D   W 15357936 + 1024 [kworker/u256:2]
8,16   0     6111     1.436530404 20685  G   W 15359984 + 1024 [kworker/u256:2]
8,16   0     6113     1.436530842 20685  I   W 15358960 + 1024 [kworker/u256:2]
8,16   0     6114     1.436531748 20685  D   W 15358960 + 1024 [kworker/u256:2]
8,16   0     6120     1.436755261 20685  I   W 15359984 + 1024 [kworker/u256:2]
8,16   0     6121     1.436756476 20685  D   W 15359984 + 1024 [kworker/u256:2]
8,16   0     6128     1.437120354     0  C   W 15356912 + 1024 [0]
8,16   0     6129     1.437121875     0  C   W 15356912 + 2048 [0]

Breakpoint 3, log_track_split (pdi=0x430260, t=0x711990) at blkparse.c:1076
1076            iot = find_track(pdi, t->pid, t->sector);
(gdb) n
1077            split = malloc(sizeof(*iot));
(gdb)
1078            split->req = iot->req;
(gdb) p split
$1 = (struct io_track *) 0x69bdd0
(gdb) p *split
$2 = {rb_node = {rb_parent_color = 6929360, rb_right = 0x0, rb_left = 0xe81bf0}, req = 0x2000d00080000, next = 0x800010000050cd, sector = 2251799813685248}

Program received signal SIGSEGV, Segmentation fault.
0x000000000040bcbc in rb_set_parent (rb=0xe81bf0, p=0x69bbd0) at rbtree.h:133
133             rb->rb_parent_color = (rb->rb_parent_color & 3) | (unsigned long)p;
(gdb) bt
 #0  0x000000000040bcbc in rb_set_parent (rb=0xe81bf0, p=0x69bbd0) at rbtree.h:133
 #1  0x000000000040c724 in rb_erase (node=0x69bdd0, root=0x430418) at rbtree.c:273
 #2  0x0000000000404810 in log_track_complete (pdi=0x430260, t=0x712810) at blkparse.c:1223
 #3  0x00000000004055e4 in log_complete (pdi=0x430260, pci=0x4bc100, t=0x712810, act=0x40cf60 "C") at blkparse.c:1518
 #4  0x0000000000405ea0 in dump_trace_fs (t=0x712810, pdi=0x430260, pci=0x4bc100) at blkparse.c:1680
 #5  0x000000000040604c in dump_trace (t=0x712810, pci=0x4bc100, pdi=0x430260) at blkparse.c:1722
 #6  0x00000000004090e8 in handle (msp=0x433cf0) at blkparse.c:2639
 #7  0x000000000040931c in do_file () at blkparse.c:2712
 #8  0x000000000040a0cc in main (argc=4, argv=0xfffffffff438) at blkparse.c:3045
(gdb) p rb
$3 = (struct rb_node *) 0xe81bf0
(gdb) p *rb
Cannot access memory at address 0xe81bf0
(gdb) up
273                     rb_set_parent(child, parent);
(gdb) p child
$4 = (struct rb_node *) 0xe81bf0
(gdb) p node
$5 = (struct rb_node *) 0x69bdd0
(gdb) p *node
$6 = {rb_parent_color = 6929360, rb_right = 0x0, rb_left = 0xe81bf0}

Signed-off-by: Kou Wenqi <kouwenqi@kylinos.cn>
Link: https://lore.kernel.org/r/tencent_DE806EEE1852F9E79115172254B8A2789207@qq.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>