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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4526e0563cesm144924535e9.1.2025.06.10.06.17.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Jun 2025 06:17:11 -0700 (PDT) Message-ID: <95d02c29-abde-4100-a670-035483e1ecc5@redhat.com> Date: Tue, 10 Jun 2025 15:17:11 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/4] userfaultfd: remove (VM_)BUG_ON()s To: Peter Xu , Tal Zussman Cc: Andrew Morton , "Jason A. Donenfeld" , Alexander Viro , Christian Brauner , Jan Kara , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20250607-uffd-fixes-v2-0-339dafe9a2fe@columbia.edu> <20250607-uffd-fixes-v2-2-339dafe9a2fe@columbia.edu> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10.06.25 15:11, Peter Xu wrote: > On Sat, Jun 07, 2025 at 02:40:01AM -0400, Tal Zussman wrote: >> BUG_ON() is deprecated [1]. Convert all the BUG_ON()s and VM_BUG_ON()s >> to use VM_WARN_ON_ONCE(). >> >> While at it, also convert the WARN_ON_ONCE()s in move_pages() to use >> VM_WARN_ON_ONCE(), as the relevant conditions are already checked in >> validate_range() in move_pages()'s caller. >> >> [1] https://www.kernel.org/doc/html/v6.15/process/coding-style.html#use-warn-rather-than-bug >> >> Signed-off-by: Tal Zussman >> --- >> fs/userfaultfd.c | 59 +++++++++++++++++++++++++------------------------- >> mm/userfaultfd.c | 66 +++++++++++++++++++++++++++----------------------------- >> 2 files changed, 61 insertions(+), 64 deletions(-) >> >> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c >> index 22f4bf956ba1..80c95c712266 100644 >> --- a/fs/userfaultfd.c >> +++ b/fs/userfaultfd.c >> @@ -165,14 +165,14 @@ static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) >> static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx) >> { >> if (refcount_dec_and_test(&ctx->refcount)) { >> - VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock)); >> - VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh)); >> - VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock)); >> - VM_BUG_ON(waitqueue_active(&ctx->fault_wqh)); >> - VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock)); >> - VM_BUG_ON(waitqueue_active(&ctx->event_wqh)); >> - VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock)); >> - VM_BUG_ON(waitqueue_active(&ctx->fd_wqh)); >> + VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_pending_wqh.lock)); >> + VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_pending_wqh)); >> + VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_wqh.lock)); >> + VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_wqh)); >> + VM_WARN_ON_ONCE(spin_is_locked(&ctx->event_wqh.lock)); >> + VM_WARN_ON_ONCE(waitqueue_active(&ctx->event_wqh)); >> + VM_WARN_ON_ONCE(spin_is_locked(&ctx->fd_wqh.lock)); >> + VM_WARN_ON_ONCE(waitqueue_active(&ctx->fd_wqh)); >> mmdrop(ctx->mm); >> kmem_cache_free(userfaultfd_ctx_cachep, ctx); > > I didn't follow closely on the latest discussions on BUG_ON, but here I > just stumbled on top of this chunk, it does look like a slight overkill > using tons of bools for each of them.. even if the doc suggested > WARN_ON_ONCE(). > > David might have a better picture of what's our plan for mm to properly > assert while reducing the overhead as much as possible. There is currently still a discussion whether VM_WARN_ON an VM_WARN_ON_ONCE could be unified. In a CONFIG_DEBUG_VM kernel, the overhead of a couple of booleans is usually the least concern (everything is big and slow already) :) > > For this specific one, if we really want to convert we could also merge > them into one, so one bool to cover all. One loses precision, but yeah, they are supposed to be found during early testing, in which case one can usually reproduce + debug fairly easily. -- Cheers, David / dhildenb