fixup! trace2: collect Windows-specific process information #117
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Guard against infinite loop while computing the parent process hierarchy. CreateToolhelp32Snapshot() is used to get a list of all processes on the system. Each process entry contains the process PID and PPID (alive at the time of the snapshot). We compute the set of ancestors of the current process by repeated searches on this list. Testing revealed that the snapshot can contain PPID cycles. This causes an infinite loop during the set construction and causes the git.exe command to hang. Testing found an instance where 3 processes were in a PPID cycle. The snapshot implied that each of these processes was its own great-grandparent. This should not be possible unless a PID was recycled and just happened to match up. For full disclosure, the Windows "System Idle Process" has PID and PPID 0. If it were to launch a Git command, it could cause a similar infinite loop. Or more properly, if any ancestor of the current Git command has PPID 0, it will appear to be a descendant of the idle process and trigger the problem. This commit fixes both cases by maintaining a list of the PIDs seen during the ancestor walk and stopping if a cycle is detected. Additionally, code was added to truncate the search after a reasonable fixed depth limit. Signed-off-by: Jeff Hostetler <[email protected]>
jeffhostetler
requested review from
dscho,
jrbriggs,
jamill,
benpeart and
kewillford
|
This change are cherry-picked from my upstream submission: gitgitgadget#108 |
jrbriggs
approved these changes
Feb 11, 2019
|
|
||
| while (find_pid(pid, hSnapshot, &pe32)) { | ||
| jw_array_string(jw, pe32.szExeFile); | ||
| if (nr_pids == NR_PIDS_LIMIT) { |
There was a problem hiding this comment.
Paranoia nit: if (nr_pids >= NR_PIDS_LIMIT) ?
There was a problem hiding this comment.
true, but we'd already have a buffer overrun at that point.
| if (!find_pid(pid, hSnapshot, &pe32)) | ||
| return; | ||
| pid = pe32.th32ParentProcessID; | ||
| /* Check for cycle in snapshot. (Yes, it happened.) */ |
There was a problem hiding this comment.
Do we need to check for cycles or should we just give up once we exceed NR_PIDS_LIMIT?
There was a problem hiding this comment.
yea, i could go either way here. my way lets us see "(cycle)" vs "(truncate)" in the Kusto data.
i thought that might be interesting.
There was a problem hiding this comment.
If we check for a cycle (which we know happens), we will avoid having NR_PIDS_LIMIT lines of repeated entries every time it does happen...
benpeart
approved these changes
Feb 11, 2019
jamill
approved these changes
Feb 11, 2019
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Guard against infinite loop while computing the parent process hierarchy.
CreateToolhelp32Snapshot() is used to get a list of all processes on the
system. Each process entry contains the process PID and PPID (alive at the
time of the snapshot). We compute the set of ancestors of the current process
by repeated searches on this list.
Testing revealed that the snapshot can contain PPID cycles. This causes an
infinite loop during the set construction and causes the git.exe command to
hang.
Testing found an instance where 3 processes were in a PPID cycle. The
snapshot implied that each of these processes was its own great-grandparent.
This should not be possible unless a PID was recycled and just happened to
match up.
For full disclosure, the Windows "System Idle Process" has PID and PPID 0.
If it were to launch a Git command, it could cause a similar infinite loop.
Or more properly, if any ancestor of the current Git command has PPID 0, it
will appear to be a descendant of the idle process and trigger the problem.
This commit fixes both cases by maintaining a list of the PIDs seen during
the ancestor walk and stopping if a cycle is detected.
Additionally, code was added to truncate the search after a reasonable fixed
depth limit.
Signed-off-by: Jeff Hostetler [email protected]