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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id bm25-20020a05620a199900b006ed138e89f2sm2409440qkb.123.2022.10.25.11.34.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Oct 2022 11:34:19 -0700 (PDT) Date: Tue, 25 Oct 2022 14:34:17 -0400 From: Peter Xu To: Axel Rasmussen Cc: Alexander Viro , Andrew Morton , Mike Kravetz , Lokesh Gidra , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] userfaultfd: wake on unregister for minor faults as well as missing Message-ID: References: <20221025182149.3076870-1-axelrasmussen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221025182149.3076870-1-axelrasmussen@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 25, 2022 at 11:21:49AM -0700, Axel Rasmussen wrote: > This was an overlooked edge case when minor faults were added. In > general, minor faults have the same rough edge here as missing faults: > if we unregister while there are waiting threads, they will just remain > waiting forever, as there is no way for userspace to wake them after > unregistration. To work around this, userspace needs to carefully wake > everything before unregistering. > > So, wake for minor faults just like we already do for missing faults as > part of the unregistration process. > > Cc: stable@vger.kernel.org > Fixes: 7677f7fd8be7 ("userfaultfd: add minor fault registration mode") > Reported-by: Lokesh Gidra > Signed-off-by: Axel Rasmussen > --- > fs/userfaultfd.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 07c81ab3fd4d..7daee4b9481c 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -1606,7 +1606,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, > start = vma->vm_start; > vma_end = min(end, vma->vm_end); > > - if (userfaultfd_missing(vma)) { > + if (userfaultfd_missing(vma) || userfaultfd_minor(vma)) { > /* > * Wake any concurrent pending userfault while > * we unregister, so they will not hang > -- > 2.38.0.135.g90850a2211-goog Thanks, Axel. Is wr-protect mode also prone to this? Would a test case help too? -- Peter Xu