From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B3298331230 for ; Tue, 23 Jun 2026 20:50:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782247823; cv=none; b=jR10p6FIdkrUQNdZ9yCyAlfu+NruLXb9lr+4E2+w7dOMNrOPMyOTLVals7CMOD2t4ZppufhLHNgJde2EwMM5iCK9JVhk0GB5kTCzKO1jE3a17uMpl8kJL9PREw0/pH4/KNNn/H1zEPA6M97L8H8asi0cIFmm0QUR0rmvYUlxPDg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782247823; c=relaxed/simple; bh=2sitsJzbeZaWKTTLflBuM3CCAlCfjdgGaDTFbIqrjPs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cKsgPs0HhcdEA6hPPAAk0V6wbIxVqF9tSz1FWOoCQXFtB2X/cKu2FvRByiwUByhKcOQrs3M2Id7N8h7SH1wLHod/bH6/bW7d3XG28mFewZOkyzE4Goy1F79Uz9oV2FQftADapwLEp7VS2Gr2XTDBNDjPXZF0m7+BsXc3wtntE9Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mCraMVCH; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mCraMVCH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F17501F000E9; Tue, 23 Jun 2026 20:50:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782247822; bh=V2seaGK6ORo3erEt5XwLFXvxM0kH+5h2nHa0PRXYaT0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=mCraMVCHAmz4Y6gtfvlzjVfnvJKRKrhffgd5Y/xs1Rwfatn8OmSmB038kEo53rUlz wM2dMiMINiwgrWb4S0G7y1122u3xJ23w10JPljpT8bskqKVisf93KuLezunI4GV1mU NQ+6+tIQu8wnvTAq0HMyIk7v3dNt62JMbGWdAeG32OYHJjFSM5hOfqxPTNS+mqpySv s9eRzpGEFE4zTQj8gyw9UfJ1T66AY6u4HUnyTTMqUzV3aXnH0VPm2sTHHF7Sr9ZG2C G+4nFaHiDws+uP+pLIwqO62MPt67SuPuow/1WOf6gvM8kTn6nzT5Qng3kMPTMSaUeQ t7UkhmZMUBUaQ== Message-ID: Date: Tue, 23 Jun 2026 22:50:19 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: debugobject: Make it work with deferred page initialization - again Content-Language: en-US To: Thomas Gleixner , LKML Cc: Vlastimil Babka , Peter Zijlstra , Alexei Starovoitov , linux-mm@vger.kernel.org, Sebastian Andrzej Siewior References: <87pl6gznti.ffs@tglx> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/7/26 14:27, Thomas Gleixner wrote: > debugobjects uses __GFP_HIGH for allocations as it might be invoked > within locked regions. That worked perfectly fine until v6.18. It still > works correctly when deferred page initialization is disabled and works > by chance when no page allocation is required before deferred page > initialization has completed. > > Since v6.18 allocations w/o a reclaim flag cause new_slab() to end up in > alloc_frozen_pages_nolock_noprof(), which returns early when deferred > page initialization has not yet completed. As the deferred page > initialization takes quite a while the debugobject pool is depleted and > debugobjects are disabled. > > This can be worked around when PREEMPT_COUNT is enabled as that allows > debugobjects to add __GFP_KSWAPD_RECLAIM to the GFP flags when the context > is preemtible. When PREEMPT_COUNT is disabled the context is unknown and > the reclaim bit can't be set because the caller might hold locks which > might deadlock in the allocator. > > In preemptible context the reclaim bit is harmless and not a performance > issue as that's usually invoked from slow path initialization context. > > That makes debugobjects depend on PREEMPT_COUNT || !DEFERRED_STRUCT_PAGE_INIT. > > Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") > Signed-off-by: Thomas Gleixner FYI, it should now be possible to revert this workaround: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=335c347686e76df9d2c7d7f61b5ea627a4c5cb4c > --- > lib/Kconfig.debug | 1 + > lib/debugobjects.c | 19 ++++++++++++++++++- > 2 files changed, 19 insertions(+), 1 deletion(-) > > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -753,6 +753,7 @@ source "mm/Kconfig.debug" > > config DEBUG_OBJECTS > bool "Debug object operations" > + depends on PREEMPT_COUNT || !DEFERRED_STRUCT_PAGE_INIT > depends on DEBUG_KERNEL > help > If you say Y here, additional code will be inserted into the > --- a/lib/debugobjects.c > +++ b/lib/debugobjects.c > @@ -398,9 +398,26 @@ static void fill_pool(void) > > atomic_inc(&cpus_allocating); > while (pool_should_refill(&pool_global)) { > + gfp_t gfp = __GFP_HIGH | __GFP_NOWARN; > HLIST_HEAD(head); > > - if (!kmem_alloc_batch(&head, obj_cache, __GFP_HIGH | __GFP_NOWARN)) > + /* > + * Allow reclaim only in preemptible context and during > + * early boot. If not preemptible, the caller might hold > + * locks causing a deadlock in the allocator. > + * > + * If the reclaim flag is not set during early boot then > + * allocations, which happen before deferred page > + * initialization has completed, will fail. > + * > + * In preemptible context the flag is harmless and not a > + * performance issue as that's usually invoked from slow > + * path initialization context. > + */ > + if (preemptible() || system_state < SYSTEM_SCHEDULING) > + gfp |= __GFP_KSWAPD_RECLAIM; > + > + if (!kmem_alloc_batch(&head, obj_cache, gfp)) > break; > > guard(raw_spinlock_irqsave)(&pool_lock); >