On 10/14/19 11:13 PM, William Brown wrote:
On 15 Oct 2019, at 15:51, Mark Reynolds <mreynolds@xxxxxxxxxx> wrote:
On 10/14/19 6:35 PM, William Brown wrote:
On 15 Oct 2019, at 06:58, Mark Reynolds <mreynolds@xxxxxxxxxx> wrote:
So we are finding these race conditions (leading to heap-use-after-free) when you stop the server while an import task is running. The current code aborts the task which leaves the database unusable until it is fully reinitialized at a later time. Unfortunately the code that handles this is complex, and very error prone.
I'd like to allow the import task to complete before fully shutting the server down. Code fix is trivial, but do we want the import to finish, or should the import be aborted (and database left broken)? Thoughts? Opinions?
The question is "what does the admin expect"? I could envisage if you start an import and then cancel the task, you expect:
* The task to be immediately stopped
* The db content rolled back.
Shouldn't we be in a betxn or similar during an import so we can revert?
Failing this, I'd assume the user would expect a ctrl-c to immediately cancel the task.
What kind of use-after-frees are we seeing?
See
https://pagure.io/389-ds-base/issue/50646
Pretty sure the first thing the import does is delete the db directory, but I have not found that in the code yet, but there are definitely no transactions used during an "import". It's a very different process. Now rolling back the database would be nice, but I can imagine very large databases(100+ million entries) where disk space could be an issue if you have to keep the old database around until the new one is imported.
As for aborting, currently there is no abort mechanism except for stopping the server. So a ctrl-C is not really an option at this time. Keep in mind I can still easily keep the current abort behavior during a shutdown, but in the current design if you abort an import the database is hosed.
What about at least hosing it but nicely somehow? So we rm db, then we start the import into some temp location, so on ctrl-c even if we crash, db is an empty dir and still mildly hosed?
I can see your point though about the db size stuff. So I guess my thinking then is:
* Could we just fix the use after free *and* make the db hosing nicer somehow?
I can fix the use-after-free, that's easy, but fixing the "hosing" is
not trivial, and it is out of the scope of what I am trying to do in 1.3.x.
* What happens if we ignore the ctrl-c and just block on import? I think someone would reach for ctrl+\ pretty fast ...
The import code launches a thread to the do the work. So hitting
control-C on a CLI tool will not stop the import, and there is currently
no abort process for Slapi Tasks that I am aware of besides creating a
new "Abort Import" task. This is something we could do in 1.4.3, or
1.5.x along with the new backend work.
Thanks,
Mark
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Sincerely,
William Brown
Senior Software Engineer, 389 Directory Server
SUSE Labs
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Sincerely,
William Brown
Senior Software Engineer, 389 Directory Server
SUSE Labs
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