From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793204221; b=egBdcmPSTPyFobHWw2S/CJAro8ATxnJ2//7ycYJL8l4HNFnSSoGdxGygAp09zAx/I7gR XPAxLlY3XFmxKah7QlZDmfLkI+JELJkgSh/n+QXUgimtbTMwcsTz5G+4iQg97DauJxHMs ptLwwnFVW2mYC6bZBu9vlDvnNKvIdrjCCzVbr4lYhM12pLz/UUJQxQPk22zZZXBJQID/1 ZdjAnd26JDmi1UTo1t6WOpAyGBUkP+7l1QqfIMChmQaXgG3pkgwaHSxSfYGy01o2/2eIl 0Q5ZhvNBQzT4+C+hGPVCAuTakdq1JrZ0jUjPTmFpFXnaTfTOMRQ+WhTpXJmftCx1GBg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793204221; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=0gKK6+kyEdy4ObANSuJOnAcVDDrpLTxw4rxdFQZ9nDc=; b=FZbND7TQGCmMjvDqaG7JOJ0kUf3tkbsAOPDBLuYdIXQVXE+xLUhwBj52snBoeiI9iu42 m/BeaB4TQ9SByDtQdYHuMcooqB5lTmYwvoHQGbuXSbLDOcVLWCGEqgA76S2spTa1kPmjB wu3XOJqJ5YceP+6jJ9BJikaWvmXq6qnMYRhSbWOH/XAU2bNH4whiYgbtcLfj+Kt7D9ueI pdPuf48IymQjEghX/e+Eqnvrr9qMpY53SlzEMOPCrwvQWCzhcCrT1CvJb6FEtwiMjMnR+ 583uXCxiDShBByDFOLbxTIoDqOvbpYfA8LhBtF9eg1hXJSzUH189WlH880d/ng0HTwQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="ibqE0/JP"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 07F7E606A31A for ; Wed, 28 Oct 2026 16:17:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=ibqE0/JP Received: by smtp.kernel.org (Postfix) with ESMTPSA id 096FD1F01825; Wed, 28 Oct 2026 16:16:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793204220; bh=0gKK6+kyEdy4ObANSuJOnAcVDDrpLTxw4rxdFQZ9nDc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ibqE0/JPcBS0Klct7XJsTVTyq427HU2F4Gt65uASd1XJlEkkOuvpw835QzWQ6dcDV hccTqLNWMz4he778kwSCBoJbCNH1qNdOieud3TvnSV1rpGDXzs6sa500KWLt0W5+er Qzd31I/T9Xx4UkyOmR940siZEezlaU+Jwsa/Ky/QkYLIJ1cjvpK2yjCtun3mV+41Fv 4lSvyRCJggvbHN9qgJAUbYq87AEfiwk2t6giPXtIsSXtEDyu56TyJU38UTAkS8q/CT 9FhSSHm4m0DR+IAMTuOpk5rSwksiRZQf4pF/0XQtl0y625EecYHSRG9enKFgNjIOWp y69X5lpLYyl5w== From: Sasha Levin To: stable@vger.kernel.org Cc: Juanlu Herrero , Anand Natarajan , Jens Axboe , Sasha Levin Subject: [PATCH 5.15.y] io_uring/poll: avoid retry wakeup loss when dropping ownership Date: Wed, 28 Oct 2026 12:16:58 -0400 Message-ID: <20261028161609.942683-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026102833-buffing-shone-0fb5@gregkh> References: <2026102833-buffing-shone-0fb5@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Juanlu Herrero [ Upstream commit 937d38dcacd675dc0572d6c9b6743960df3128ed ] If a wakeup sets IO_POLL_RETRY_FLAG between the owning task consuming the existing instance of IO_POLL_RETRY_FLAG and the loop check of io_poll_check_events(), then we stall on processing the request until an unrelated wakeup comes along. Using atomic_cmpxchg instead of atomic_sub_return to guarantee both the count v and poll_refs are 0 and no wake-ups are missed. Cc: stable@vger.kernel.org Fixes: a26a35e9019f ("io_uring: make poll refs more robust") Signed-off-by: Juanlu Herrero Assisted-by: LLM Suggested-by: Anand Natarajan Link: https://patch.msgid.link/20261013-pu-cmpxchg-v1-1-4ddc10fd8a03@fastmail.com Signed-off-by: Jens Axboe [ sashal: Relocated the change to io_poll_check_events() in the monolithic io_uring implementation. ] Signed-off-by: Sasha Levin --- io_uring/io_uring.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 8d5791d8f4031..a87b24c77c0ee 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -5690,8 +5690,8 @@ static int io_poll_check_events(struct io_kiocb *req) * Release all references, retry if someone tried to restart * task_work while we were executing it. */ - } while (atomic_sub_return(v & IO_POLL_REF_MASK, &req->poll_refs) & - IO_POLL_REF_MASK); + v &= IO_POLL_REF_MASK; + } while (atomic_cmpxchg(&req->poll_refs, v, 0) != v); return 1; } -- 2.53.0