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Date: Sat, 25 May 2019 08:33:13 -0700 From: Randy Dunlap <rdunlap@...radead.org> To: Kees Cook <keescook@...omium.org> Cc: LKML <linux-kernel@...r.kernel.org>, Dan Carpenter <dan.carpenter@...cle.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, Matthew Wilcox <willy@...radead.org>, Linux MM <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: lib/test_overflow.c causes WARNING and tainted kernel On 3/13/19 7:53 PM, Kees Cook wrote: > Hi! > > On Wed, Mar 13, 2019 at 2:29 PM Randy Dunlap <rdunlap@...radead.org> wrote: >> >> This is v5.0-11053-gebc551f2b8f9, MAR-12 around 4:00pm PT. >> >> In the first test_kmalloc() in test_overflow_allocation(): >> >> [54375.073895] test_overflow: ok: (s64)(0 << 63) == 0 >> [54375.074228] WARNING: CPU: 2 PID: 5462 at ../mm/page_alloc.c:4584 __alloc_pages_nodemask+0x33f/0x540 >> [...] >> [54375.079236] ---[ end trace 754acb68d8d1a1cb ]--- >> [54375.079313] test_overflow: kmalloc detected saturation > > Yup! This is expected and operating as intended: it is exercising the > allocator's detection of insane allocation sizes. :) > > If we want to make it less noisy, perhaps we could add a global flag > the allocators could check before doing their WARNs? > > -Kees I didn't like that global flag idea. I also don't like the kernel becoming tainted by this test. Would it make sense to change the WARN_ON_ONCE() to a call to warn_alloc() instead? or use a plain raw printk_once()? warn_alloc() does the _NOWARN check and does rate limiting. --- lnx-51-rc2.orig/mm/page_alloc.c +++ lnx-51-rc2/mm/page_alloc.c @@ -4581,7 +4581,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, u * so bail out early if the request is out of bound. */ if (unlikely(order >= MAX_ORDER)) { - WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)); + warn_alloc(gfp_mask, NULL, + "page allocation failure: order:%u", order); return NULL; } -- ~Randy
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