Messages in this thread | | | Subject | Re: [PATCH] kmemleak: Fix scheduling-while-atomic bug | From | Catalin Marinas <> | Date | Wed, 01 Jul 2009 10:46:31 +0100 |
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On Wed, 2009-07-01 at 11:30 +0200, Ingo Molnar wrote: > * Catalin Marinas <catalin.marinas@arm.com> wrote: > > > > The minimal fix below removes scan_yield() and adds a > > > cond_resched() to the outmost (safe) place of the scanning > > > thread. This solves the regression. > > > > With CONFIG_PREEMPT disabled it won't reschedule during the bss > > scanning but I don't see this as a real issue (task stacks > > scanning probably takes longer anyway). > > Yeah. I suspect one more cond_resched() could be added - i just > didnt see an obvious place for it, given that scan_block() is being > called with asymetric held-locks contexts.
Yes, scan_block shouldn't call cond_resched(). The code is cleaner if functions don't have too many side-effects. I can see about 1 sec of bss scanning on an ARM board but with processor at < 500MHz and slow memory system. On a standard x86 systems BSS scanning may not be noticeable (and I think PREEMPT enabling is quite common these days).
Since we are at locking, I just noticed this on my x86 laptop when running cat /sys/kernel/debug/kmemleak (I haven't got it on an ARM board):
================================================ [ BUG: lock held when returning to user space! ] ------------------------------------------------ cat/3687 is leaving the kernel with locks still held! 1 lock held by cat/3687: #0: (scan_mutex){+.+.+.}, at: [<c01e0c5c>] kmemleak_open+0x3c/0x70
kmemleak_open() acquires scan_mutex and unconditionally releases it in kmemleak_release(). The mutex seems to be released as a subsequent acquiring works fine.
Is this caused just because cat may have exited without closing the file descriptor (which should be done automatically anyway)?
Thanks.
-- Catalin
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