From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [BUG] SLOB's krealloc() seems bust From: Matt Mackall In-Reply-To: References: <1223387841.26330.36.camel@lappy.programming.kicks-ass.net> <48EB6D2C.30806@linux-foundation.org> <1223391655.13453.344.camel@calx> <1223395846.26330.55.camel@lappy.programming.kicks-ass.net> <1223397455.13453.385.camel@calx> <1223403082.26330.78.camel@lappy.programming.kicks-ass.net> Content-Type: text/plain Date: Wed, 08 Oct 2008 14:51:57 -0500 Message-Id: <1223495517.17706.31.camel@calx> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Peter Zijlstra , Christoph Lameter , linux-mm , Nick Piggin , Ingo Molnar , linux-kernel , akpm , Pekka J Enberg List-ID: 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 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. -- 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