Messages in this thread | | | Subject | Re: [BUG] SLOB's krealloc() seems bust | From | Matt Mackall <> | Date | Wed, 08 Oct 2008 00:15:47 -0500 |
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On Wed, 2008-10-08 at 16:11 +1100, Nick Piggin wrote: > On Wednesday 08 October 2008 15:54, Nick Piggin wrote: > > On Wednesday 08 October 2008 15:46, Matt Mackall wrote: > > > On Wed, 2008-10-08 at 15:22 +1100, Nick Piggin wrote: > > > > On Wednesday 08 October 2008 10:08, Matt Mackall wrote: > > > > > > diff -r 5e32b09a1b2b mm/slob.c > > > > > --- a/mm/slob.c Fri Oct 03 14:04:43 2008 -0500 > > > > > +++ b/mm/slob.c Tue Oct 07 18:05:15 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 + 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); /* round up */ > > > > > + } else > > > > > return sp->page.private; > > > > > } > > > > > > > > Yes, I came up with nearly the same patch before reading this > > > > > > > > --- linux-2.6/mm/slob.c 2008-10-08 14:43:17.000000000 +1100 > > > > +++ suth/mm/slob.c 2008-10-08 15:11:06.000000000 +1100 > > > > @@ -514,9 +514,11 @@ size_t ksize(const void *block) > > > > 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 *m + align; > > > > + } else > > > > return sp->page.private; > > > > } > > > > > > > > However, mine is lifted directly from kfree, wheras you do something a > > > > bit different. Hmm, ksize arguably could be used to find the underlying > > > > allocated slab size in order to use a little bit more than we'd asked > > > > for. So probably we should really just `return *m` (don't round up or > > > > add any padding). > > > > > > Huh? ksize should report how much space is available in the buffer. If > > > we request 33 bytes from SLUB and it gives us 64, ksize reports 64. If > > > we request 33 bytes from SLOB and it gives us 34, we should report 34. > > > > Oh.. hmm yeah right, I didn't realise what you were doing there. > > OK, so your patch looks good to me then (provided it is diffed against > > the previous one, for Linus). > > OK, no, that's why I got confused. SLOB_UNITS will round you up to the > next SLOB_UNIT. You'd then have to multiply by SLOB_UNIT to get back to > bytes.
Damnit, how many ways can we get confused by these little details? I'll spin a final version and run it against the test harness shortly.
-- Mathematics is the supreme nostalgia of our time.
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