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Mon, 03 Feb 2020 15:17:50 -0500 X-MC-Unique: LVTmi57UP5CtwO7-hrd4wA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B667D13E5; Mon, 3 Feb 2020 20:17:48 +0000 (UTC) Received: from mail (ovpn-120-67.rdu2.redhat.com [10.10.120.67]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0D78B1001B09; Mon, 3 Feb 2020 20:17:46 +0000 (UTC) From: Andrea Arcangeli To: Will Deacon , Catalin Marinas , Jon Masters , Rafael Aquini , Mark Salter Subject: [PATCH 1/2] mm: use_mm: fix for arches checking mm_users to optimize TLB flushes Date: Mon, 3 Feb 2020 15:17:44 -0500 Message-Id: <20200203201745.29986-2-aarcange@redhat.com> In-Reply-To: <20200203201745.29986-1-aarcange@redhat.com> References: <20200203201745.29986-1-aarcange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200203_121944_740235_A18F64A6 X-CRM114-Status: GOOD ( 10.02 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org alpha, ia64, mips, powerpc, sh, sparc are relying on a check on mm->mm_users to know if they can skip some remote TLB flushes for single threaded processes. Most callers of use_mm() tend to invoke mmget_not_zero() or get_task_mm() before use_mm() to ensure the mm will remain alive in between use_mm() and unuse_mm(). Some callers however don't increase mm_users and they instead rely on serialization in __mmput() to ensure the mm will remain alive in between use_mm() and unuse_mm(). Not increasing mm_users during use_mm() is however unsafe for aforementioned arch TLB flushes optimizations. So either mmget()/mmput() should be added to the problematic callers of use_mm()/unuse_mm() or we can embed them in use_mm()/unuse_mm() which is more robust. Signed-off-by: Andrea Arcangeli --- mm/mmu_context.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/mmu_context.c b/mm/mmu_context.c index 3e612ae748e9..ced0e1218c0f 100644 --- a/mm/mmu_context.c +++ b/mm/mmu_context.c @@ -30,6 +30,7 @@ void use_mm(struct mm_struct *mm) mmgrab(mm); tsk->active_mm = mm; } + mmget(mm); tsk->mm = mm; switch_mm(active_mm, mm, tsk); task_unlock(tsk); @@ -57,6 +58,7 @@ void unuse_mm(struct mm_struct *mm) task_lock(tsk); sync_mm_rss(mm); tsk->mm = NULL; + mmput(mm); /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); task_unlock(tsk); _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel