Messages in this thread Patch in this message | | | Subject | Re: [BUG] SLOB's krealloc() seems bust | From | Matt Mackall <> | Date | Wed, 08 Oct 2008 14:51:57 -0500 |
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On Tue, 2008-10-07 at 11:18 -0700, Linus Torvalds wrote: > > On Tue, 7 Oct 2008, Peter Zijlstra wrote: > > > On Tue, 2008-10-07 at 10:57 -0700, Linus Torvalds wrote: > > > > > Peter - can you check with that > > > > > > > if (slob_page(sp)) > > > > - return ((slob_t *)block - 1)->units + SLOB_UNIT; > > > > + return (((slob_t *)block - 1)->units - 1) * SLOB_UNIT; > > > > > > thing using > > > > > > - return ((slob_t *)block - 1)->units + SLOB_UNIT; > > > + return ((slob_t *)block - 1)->units * SLOB_UNIT; > > > > > > instead? > > > > went splat on the second run... > > Well, that makes it simple. I'll take Matt's patch as being "tested", and > somebody can hopefully explain where the extra unit comes from later.
Ok, I think we've gotten to the bottom of this. Here's an incremental patch that doesn't work by dumb luck. Please apply.
SLOB: fix bogus ksize calculation fix
This fixes the previous fix, which was completely wrong on closer inspection. This version has been manually tested with a user-space test harness and generates sane values. A nearly identical patch has been boot-tested.
The problem arose from changing how kmalloc/kfree handled alignment padding without updating ksize to match. This brings it in sync.
Signed-off-by: Matt Mackall <mpm@selenic.com>
diff -r 3dd2424d4c32 -r 73d55a1b6c10 mm/slob.c --- a/mm/slob.c Tue Oct 07 23:00:11 2008 +0000 +++ b/mm/slob.c Wed Oct 08 14:48:45 2008 -0500 @@ -514,9 +514,11 @@ return 0; sp = (struct slob_page *)virt_to_page(block); - if (slob_page(sp)) - return (((slob_t *)block - 1)->units - 1) * SLOB_UNIT; - else + if (slob_page(sp)) { + int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN); + unsigned int *m = (unsigned int *)(block - align); + return SLOB_UNITS(*m) * SLOB_UNIT; + } else return sp->page.private; }
-- Mathematics is the supreme nostalgia of our time.
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