Red Hat Bugzilla – Bug 154639
kernel thread current->mm dereference in grab_swap_token causes oops
Last modified: 2007-11-30 17:07:17 EST
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Description of problem:
Veritas has a kernel thread that performs asynchronous direct i/o on behalf of user programs. When the i/o data is available the kernel thread calls get_user_pages(), to make sure the user pages are present before moving the
data into user buffers. A side effect of that is, if the user program happens to be paged out, we end up in grab_swap_token, with current->mm set to NULL. Unfortunately the code dereferences current->mm without checking whether it is NULL.
stack functions back trace :-
A suitable fix would be to add the following to start of grab_swap_token()
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Install veritas software stack onto system
2. Run Veritas' Oracle Data Manager stress suite
Actual Results: After several hours and under heavy stress the system oops in grab_swap_token()
Expected Results: Function should just return if current->mm is NULL *or* allow an mm_sruct pointer
to be passed in as an argument. However, it still needs to check for mm_struct
pointer being NULL.
I'll submit a (trivial) patch for the RHEL4 kernel to ignore a current->mm of NULL.
Btw, note that for most kernel threads current->mm tends to be &init_mm...
Btw, have you verified that adding the check really fixes the issue, or does the
kernel simply crash elsewhere? I am not 100% sure that running any task with a
NULL ->mm is valid...
When calling daemonize() to create a kernel thread, it calls exit_mm().
This sets tsk->mm to NULL and the thread/process runs with a 'lazy_tlb'.
Also, I thought all kernel threads didn't have an address space, hence mm
is supposed to be NULL.
You're right. Hmmm, I could've sworn they got moved to &init_mm.
Anyway, the patch has been submitted for inclusion into RHEL4 yesterday, and got
approved. Thank you for alerting us to this bug.
I have run a Veritas specific stress test (odmstress) non-stop for over 100
hours with this patch fix (U1-kernel-2.6.9-6.43) and the testing was successful.
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.