From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 1FD34286422 for ; Tue, 19 Aug 2025 08:56:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755593799; cv=none; b=RwNeZCmhq3oaq2VWQl07OzzRKiTqDDsOtZY4Gh+sigwOUf6+TeWbDPKuSqLNdyPzOkt/mdC7ItvCUBD/9Vg0hnFBpEPLCpK15vviE/sqZZOj7ZDX02BU37/bKL/Q4pMdDPf3n9M+Lvt7BzhjkuTjvh/z0v40sazZKt0O/K1THuU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755593799; c=relaxed/simple; bh=+9+nYZEEg+Neh/L38A5bN1p9F4RyH1s/bG69HtLDK6U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NWrsB4X3w+thnm4eQc9rASEla1NjK4SpaTDVMjuGlHgYmRjOGGYqKlObW2TRNukcAbVWhCda/pPV1goF3jh2wpPPg26B0Krs5dxpnog0GSMeyK+7Cvr9HHPtDzneDL6/RO0BTtjPU5a5us1stedEPWnGQOYNdQEo/yb9XzC30VU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=J/EBz61F; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="J/EBz61F" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755593797; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=+ibUK4q/Rvy3c7fBEbcTRGpKubTCINpqdPqllT/qlSY=; b=J/EBz61FtuILNCyjEQcdn+qDf9tj+MJNqPa6XkymZetA4m61FWYTC0OtYsfXJhMIawful5 29DeiPaOJzThHwm4gTMCLHuSnynzrTDvXHTBZjPazxNGoe2scMN26FxkC5V7YbG9pG+eLT Fb6DDwHQVVCz8IYLumZbKMZ+yC/Eejo= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-79-1ws7qeZ_Mk-k-aFR6OJIpA-1; Tue, 19 Aug 2025 04:56:33 -0400 X-MC-Unique: 1ws7qeZ_Mk-k-aFR6OJIpA-1 X-Mimecast-MFC-AGG-ID: 1ws7qeZ_Mk-k-aFR6OJIpA_1755593791 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AB162180048E; Tue, 19 Aug 2025 08:56:31 +0000 (UTC) Received: from localhost (unknown [10.72.112.239]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9C2291800280; Tue, 19 Aug 2025 08:56:29 +0000 (UTC) Date: Tue, 19 Aug 2025 16:56:25 +0800 From: Baoquan He To: Uladzislau Rezki Cc: linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Michal Hocko , LKML Subject: Re: [PATCH 6/8] mm/vmalloc: Defer freeing partly initialized vm_struct Message-ID: References: <20250807075810.358714-1-urezki@gmail.com> <20250807075810.358714-7-urezki@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On 08/18/25 at 03:02pm, Uladzislau Rezki wrote: > On Mon, Aug 18, 2025 at 12:21:15PM +0800, Baoquan He wrote: > > On 08/07/25 at 09:58am, Uladzislau Rezki (Sony) wrote: > > > __vmalloc_area_node() may call free_vmap_area() or vfree() on > > > error paths, both of which can sleep. This becomes problematic > > > if the function is invoked from an atomic context, such as when > > > GFP_ATOMIC or GFP_NOWAIT is passed via gfp_mask. > > > > > > To fix this, unify error paths and defer the cleanup of partly > > > initialized vm_struct objects to a workqueue. This ensures that > > > freeing happens in a process context and avoids invalid sleeps > > > in atomic regions. > > > > > > Signed-off-by: Uladzislau Rezki (Sony) > > > --- > > > include/linux/vmalloc.h | 6 +++++- > > > mm/vmalloc.c | 34 +++++++++++++++++++++++++++++++--- > > > 2 files changed, 36 insertions(+), 4 deletions(-) > > > > > > diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h > > > index fdc9aeb74a44..b1425fae8cbf 100644 > > > --- a/include/linux/vmalloc.h > > > +++ b/include/linux/vmalloc.h > > > @@ -50,7 +50,11 @@ struct iov_iter; /* in uio.h */ > > > #endif > > > > > > struct vm_struct { > > > - struct vm_struct *next; > > > + union { > > > + struct vm_struct *next; /* Early registration of vm_areas. */ > > > + struct llist_node llnode; /* Asynchronous freeing on error paths. */ > > > + }; > > > + > > > void *addr; > > > unsigned long size; > > > unsigned long flags; > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > index 7f48a54ec108..2424f80d524a 100644 > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > > @@ -3680,6 +3680,35 @@ vm_area_alloc_pages(gfp_t gfp, int nid, > > > return nr_allocated; > > > } > > > > > > +static LLIST_HEAD(pending_vm_area_cleanup); > > > +static void cleanup_vm_area_work(struct work_struct *work) > > > +{ > > > + struct vm_struct *area, *tmp; > > > + struct llist_node *head; > > > + > > > + head = llist_del_all(&pending_vm_area_cleanup); > > > + if (!head) > > > + return; > > > + > > > + llist_for_each_entry_safe(area, tmp, head, llnode) { > > > + if (!area->pages) > > > + free_vm_area(area); > > > + else > > > + vfree(area->addr); > > > + } > > > +} > > > + > > > +/* > > > + * Helper for __vmalloc_area_node() to defer cleanup > > > + * of partially initialized vm_struct in error paths. > > > + */ > > > +static DECLARE_WORK(cleanup_vm_area, cleanup_vm_area_work); > > > +static void defer_vm_area_cleanup(struct vm_struct *area) > > > +{ > > > + if (llist_add(&area->llnode, &pending_vm_area_cleanup)) > > > + schedule_work(&cleanup_vm_area); > > > +} > > > > Wondering why here we need call schudule_work() when > > pending_vm_area_cleanup was empty before adding new entry. Shouldn't > > it be as below to schedule the job? Not sure if I miss anything. > > > > if (!llist_add(&area->llnode, &pending_vm_area_cleanup)) > > schedule_work(&cleanup_vm_area); > > > > ===== > > /** > > * llist_add - add a new entry > > * @new: new entry to be added > > * @head: the head for your lock-less list > > * > > * Returns true if the list was empty prior to adding this entry. > > */ > > static inline bool llist_add(struct llist_node *new, struct llist_head *head) > > { > > return llist_add_batch(new, new, head); > > } > > ===== > > > But then you will not schedule. If the list is empty, we add one element > llist_add() returns 1, but your condition expects 0. > > How it works: > > If someone keeps adding to the llist and it is not empty we should not > trigger a new work, because a current work is in flight(it will cover new comers), > i.e. it has been scheduled but it has not yet completed llist_del_all() on > the head. > > Once it is done, a new comer will trigger a work again only if it sees NULL, > i.e. when the list is empty. Fair enough. I thought it's a deferring work, in fact it's aiming to put the error handling in a workqueue, but not the current atomic context. Thanks for the explanation.