From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [BUG] SLOB's krealloc() seems bust From: Matt Mackall In-Reply-To: <200810081611.30897.nickpiggin@yahoo.com.au> References: <1223387841.26330.36.camel@lappy.programming.kicks-ass.net> <1223441190.13453.459.camel@calx> <200810081554.33651.nickpiggin@yahoo.com.au> <200810081611.30897.nickpiggin@yahoo.com.au> Content-Type: text/plain Date: Wed, 08 Oct 2008 00:15:47 -0500 Message-Id: <1223442947.13453.462.camel@calx> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Pekka Enberg , Peter Zijlstra , Christoph Lameter , linux-mm , Linus Torvalds , Ingo Molnar , linux-kernel , akpm List-ID: 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org