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Thu, 27 Nov 2025 05:48:38 -0500 X-MC-Unique: 5AiSjQbEOhiA10wojh9Pcg-1 X-Mimecast-MFC-AGG-ID: 5AiSjQbEOhiA10wojh9Pcg_1764240517 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2D2B7180045C; Thu, 27 Nov 2025 10:48:36 +0000 (UTC) Received: from localhost (unknown [10.72.112.107]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6B9AA195608E; Thu, 27 Nov 2025 10:48:33 +0000 (UTC) Date: Thu, 27 Nov 2025 18:48:29 +0800 From: Baoquan He To: Youngjun Park Cc: akpm@linux-foundation.org, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, baohua@kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 1/2] mm/swapfile: fix list iteration when next node is removed during discard Message-ID: References: <20251127100303.783198-1-youngjun.park@lge.com> <20251127100303.783198-2-youngjun.park@lge.com> MIME-Version: 1.0 In-Reply-To: <20251127100303.783198-2-youngjun.park@lge.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: sUfnAnGov96tSZT3m0-vhwHNQV3eCqzV2c_dt17hcNI_1764240517 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Queue-Id: 225D740006 X-Rspamd-Server: rspam11 X-Stat-Signature: aq1aywiyt16g7jga9ac1bm98h33wjbnu X-HE-Tag: 1764240521-148031 X-HE-Meta: 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 GtI3qwjE 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/27/25 at 07:03pm, Youngjun Park wrote: > When the next node is removed from the plist (e.g. by swapoff), > plist_del() makes the node point to itself, causing the iteration to > loop on the same entry indefinitely. > > Add a plist_node_empty() check to detect this case and restart > iteration, allowing swap_sync_discard() to continue processing > remaining swap devices that still have pending discard entries. > > Additionally, switch from swap_avail_lock/swap_avail_head to > swap_lock/swap_active_head so that iteration is only affected by > swapoff operations rather than frequent availability changes, > reducing exceptional condition checks and lock contention. > > Fixes: 686ea517f471 ("mm, swap: do not perform synchronous discard during allocation") > Suggested-by: Kairui Song > Acked-by: Kairui Song > Signed-off-by: Youngjun Park > --- > mm/swapfile.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) Reviewed-by: Baoquan He > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index d12332423a06..8116f36e440b 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1387,9 +1387,10 @@ static bool swap_sync_discard(void) > bool ret = false; > struct swap_info_struct *si, *next; > > - spin_lock(&swap_avail_lock); > - plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) { > - spin_unlock(&swap_avail_lock); > + spin_lock(&swap_lock); > +start_over: > + plist_for_each_entry_safe(si, next, &swap_active_head, list) { > + spin_unlock(&swap_lock); > if (get_swap_device_info(si)) { > if (si->flags & SWP_PAGE_DISCARD) > ret = swap_do_scheduled_discard(si); > @@ -1397,9 +1398,12 @@ static bool swap_sync_discard(void) > } > if (ret) > return true; > - spin_lock(&swap_avail_lock); > + > + spin_lock(&swap_lock); > + if (plist_node_empty(&next->list)) > + goto start_over; > } > - spin_unlock(&swap_avail_lock); > + spin_unlock(&swap_lock); > > return false; > } > -- > 2.34.1 >