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b=scI0iS31p3r/2zgmu76sbJ2EW57b76Bwi6195T8GsKljBBOukLTZDp9ZQdyhBkGCc nIGSGLldvglCrMJe28eD7d3PnxziysU11HQE18UiSKP4SUys3FZOtNDPrujfHzaK9k BOkVNig+v+YnL/zGYheFNs/vMmqgX/C8uWI5xh0s3qwERargkFEU/BNLlMz6IF8Ml5 yu+xl1rL4Iom0LgXbgYwHgkJegIxFADYBZ0yQXma7qUC6I0fj4jDJMJhZmE4LjdxLw r91WLG3CSLavRllAQNe27gMq8NbhTDyD7cbrMZo7BuPbD18dafhJCaqNru/agGxb7O GIOnAPCtWAM7w== Date: Mon, 11 May 2026 13:48:04 +0300 From: Mike Rapoport To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Alexander Viro , Christian Brauner , Jan Kara , Peter Xu , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 1/3] userfaultfd: ensure mremap_userfaultfd_fail() releases mmap_changing Message-ID: References: <20260501145433.156211-1-rppt@kernel.org> <20260501145433.156211-2-rppt@kernel.org> <3a04ae6a-049f-4d3d-b5c9-e60e86be8e5a@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3a04ae6a-049f-4d3d-b5c9-e60e86be8e5a@kernel.org> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1C515160006 X-Stat-Signature: wn1dtpqhmyeh4ppy9ismfmqicgiwon8q X-Rspam-User: X-HE-Tag: 1778496492-867560 X-HE-Meta: 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 aEiFsdAg /ZQGfxremEeyt9FLOpYuUoRpbW89SPU9J+awHj26FMOk41mDF6Ic0hC4kO9ekbIzfm5cSyOdg3T3+GCaS1rUfhbUG5uj5MoT50azuk8n/1GOwupL8ki8IgKnnLSX5QlLV1HpL4fOuJvP758xvWYDLStw9pnkW3jOJhTRqkO1aW8Bf/schdvHrGhc04QrPIvlWjCumcNBMw7lgicurWuYseukpKb0uXPRpgjEUsNVqakWqAy+U6sjUBIAhgmQO4e0Dlar+cT54PF247DPf1qOsr23xLn342Ro9bw1wjJYE3KomSWgmag7zChgdWyCW4+7janXBaT8c9g7eJHPPR98CMjhTQeoAqggcu9MtTJ6XvZo11PjGEIAp8N1gvH0Hn2eplcJQ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, May 11, 2026 at 11:15:34AM +0200, David Hildenbrand (Arm) wrote: > On 5/1/26 16:54, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" > > > > Sashiko says: > > > > mremap_userfaultfd_prep() increments ctx->mmap_changing to stall > > concurrent operations, but mremap_userfaultfd_fail() does not > > decrement it before dropping the context reference. > > > > If an mremap operation fails, ctx->mmap_changing remains elevated. This > > will causes subsequent userfaultfd operations like a UFFDIO_COPY to fail > > with -EAGAIN. > > > > Sounds like we should CC stable? Yes. > > Decrement ctx->mmap_changing in mremap_userfaultfd_fail(). > > > > Link: https://sashiko.dev/#/patchset/20260430113512.115938-1-rppt@kernel.org > > Fixes: df2cc96e7701 ("userfaultfd: prevent non-cooperative events vs mcopy_atomic races") > > Signed-off-by: Mike Rapoport (Microsoft) > > --- > > fs/userfaultfd.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > > index 4b53dc4a3266..ef963a58f1a1 100644 > > --- a/fs/userfaultfd.c > > +++ b/fs/userfaultfd.c > > @@ -786,6 +786,7 @@ void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx) > > if (!ctx) > > return; > > > > + atomic_dec(&ctx->mmap_changing); > > I'll note that other users have a > > VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0); > > In there. Likely we should do the same? Yeah, we could. > -- > Cheers, > > David -- Sincerely yours, Mike.