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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=OSFcPHbwPU7VuQqTvb7CRygx4qEQJSCX4opQ3eOpE/E=; b=H7SsWVFAs+UU5vBKh63aHolXUa2QZpiPqzpHah/V57rz9PPdhxmVSAo7LOSWuEwqeh 3APvw63nclBgMdVO1n20pwS9kxZeQsg2a3tM/r00NWN/ywYm0DQQlfVRvnMyEJ8ZOXd9 vu+e5b4vmfhxKnZ+wk9ObgAsf1eiERtKxoNkSiHkC3h+SKcCEDDjulAVqwl9tIF9Qwj0 MM0OdWqnni7DU0yCaft3K6OODn0NlgBD2tJBB8Jmn5m+LRU7mPRhNXjOWvTMSF5yLPC2 VRhPFw2avDVMk8tGkpLbk2HxcEaM11uCWXNnzs4BEIVsTw2ASeBosexeTh6mwTeczWCx B6lA== X-Gm-Message-State: AFqh2koAeMOCvu7MEypYhDXwS0iSdcTIQ/+kQw+U3QUX7SBIscwKnO6V uBCAZL/ZRDKAUnTmel+MLzAjTDzLsiex7mpOL9Bm8A== X-Google-Smtp-Source: AMrXdXtN2czWy7s7z6riYeL+TaWTkUjkEXdbo5Qe/e5v9zxAXm+Abj+Br8dn7RO1A0aNN2qhpP5AND12ti3Cn4146c8= X-Received: by 2002:a92:c5c6:0:b0:30c:877:db26 with SMTP id s6-20020a92c5c6000000b0030c0877db26mr453316ilt.101.1673985097438; Tue, 17 Jan 2023 11:51:37 -0800 (PST) MIME-Version: 1.0 References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-33-surenb@google.com> In-Reply-To: <20230109205336.3665937-33-surenb@google.com> From: Jann Horn Date: Tue, 17 Jan 2023 20:51:01 +0100 Message-ID: Subject: Re: [PATCH 32/41] mm: prevent userfaults to be handled under per-vma lock To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 5xo1m46snocqkayc83crrmxe5jecx787 X-Rspamd-Queue-Id: 554FF1A0007 X-HE-Tag: 1673985098-273227 X-HE-Meta: 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 7c4rQaXc 6jhQG0tUF8GrFscs= 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: On Mon, Jan 9, 2023 at 9:55 PM Suren Baghdasaryan wrote: > Due to the possibility of handle_userfault dropping mmap_lock, avoid fault > handling under VMA lock and retry holding mmap_lock. This can be handled > more gracefully in the future. > > Signed-off-by: Suren Baghdasaryan > Suggested-by: Peter Xu > --- > mm/memory.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/mm/memory.c b/mm/memory.c > index 20806bc8b4eb..12508f4d845a 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5273,6 +5273,13 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, > if (!vma->anon_vma) > goto inval; > > + /* > + * Due to the possibility of userfault handler dropping mmap_lock, avoid > + * it for now and fall back to page fault handling under mmap_lock. > + */ > + if (userfaultfd_armed(vma)) > + goto inval; This looks racy wrt concurrent userfaultfd_register(). I think you'll want to do the userfaultfd_armed(vma) check _after_ locking the VMA, and ensure that the userfaultfd code write-locks the VMA before changing the __VM_UFFD_FLAGS in vma->vm_flags. > if (!vma_read_trylock(vma)) > goto inval; > > -- > 2.39.0 >