Re: [Crash-utility] [PATCH] Add ending identifier for task structure parsing
On 2022/08/24 13:06, Tao Liu wrote:
Previously, the ending identifier for parsing the task structure
member is " }, \n". However the ending identifier is not always
as expected. " },\n" can also be the ending identifier. For example,
if we have the following struct, the parsing will fail.
tasks = {\n
next = 0xffff94f8038f8838,\n
prev = 0xffff94f8036f8838\n
},\n
Before:
crash> task -R tasks ffff94f8038f4000
PID: 847 TASK: ffff94f8038f4000 CPU: 72 COMMAND: "khungtaskd"
Good catch!
but it looks like the cause is that crash cannot detect the closing
brace of a union? For example,
crash-dev> task 1
PID: 1 TASK: ffff8f96c159c8c0 CPU: 15 COMMAND: "systemd"
struct task_struct {
thread_info = {
flags = 0,
status = 0
},
state = 1,
stack = 0xffff9b6dc017c000,
{
usage = {
refs = {
counter = 1
}
},
rh_kabi_hidden_616 = {
usage = {
counter = 1
}
},
{<No data fields>}
}, <<-- This
flags = 4194560,
ptrace = 0,
wake_entry = {
next = 0x0
},
on_cpu = 0,
As a result, the randomized switch is always on after this, and
lookfor1 (and 2) will become wrong.
So "task -R" can show task_struct.thread_info and cannot show
task_struct.wake_entry, because the latter is after the union.
crash-dev> task -R thread_info 1
PID: 1 TASK: ffff8f96c159c8c0 CPU: 0 COMMAND: "systemd"
thread_info = {
flags = 0,
status = 0
},
crash-dev> task -R wake_entry 1
PID: 1 TASK: ffff8f96c159c8c0 CPU: 0 COMMAND: "systemd"
And upstream kernels (not randomized) don't have a union before
the task_struct.tasks, the issue is not reproducible with it.
crash-dev> task -R tasks 1
PID: 1 TASK: ffff9d1a4081b400 CPU: 3 COMMAND: "systemd"
tasks = {
next = 0xffff9d1a4081d678,
prev = 0xffffffff9a8191b8 <init_task+2168>
},
but anyway reproducible with a member after a union.
crash-dev> struct task_struct
...
union {
refcount_t rcu_users;
struct callback_head rcu;
};
struct pipe_inode_info *splice_pipe;
crash-dev> task -R splice_pipe 1
PID: 1 TASK: ffff9d1a4081b400 CPU: 3 COMMAND: "systemd"
So please check if this is correct and fix the commit log.
After:
crash> task -R tasks ffff94f8038f4000
PID: 847 TASK: ffff94f8038f4000 CPU: 72 COMMAND: "khungtaskd"
tasks = {
next = 0xffff94f8038f8838,
prev = 0xffff94f8036f8838
},
Signed-off-by: Tao Liu <ltao(a)redhat.com>
---
task.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/task.c b/task.c
index 071c787..db2abc8 100644
--- a/task.c
+++ b/task.c
@@ -3436,7 +3436,8 @@ parse_task_thread(int argcnt, char *arglist[], struct task_context
*tc) {
while (fgets(buf, BUFSIZE, pc->tmpfile)) {
if (STREQ(buf, " {\n"))
randomized = TRUE;
- else if (randomized && STREQ(buf, " }, \n"))
+ else if (randomized &&
+ (STREQ(buf, " }, \n") || STREQ(buf, " },\n")))
randomized = FALSE;
Looks fine but it looks like gdb-10.2 does not print a space before "\n",
I think we can _replace_ the STREQ(), not add, because the current branch
only supports gdb-10.2.
Thanks,
Kazu