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Howlett" , Peter Zijlstra , Andrew Morton , Andy Lutomirski , Borislav Petkov , Daniel Gomez , Dave Hansen , Ingo Molnar , Luis Chamberlain , Mark Rutland , Masami Hiramatsu , "H. Peter Anvin" , Petr Pavlu , Sami Tolvanen , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH 3/8] execmem: rework execmem_cache_free() Message-ID: References: <20250704134943.3524829-1-rppt@kernel.org> <20250704134943.3524829-4-rppt@kernel.org> <20250707111102.GF1613200@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: kctqe8r7otdgtqua6gwyy1ff1s57j4sn X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 75391140004 X-HE-Tag: 1751901158-688252 X-HE-Meta: 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 mrPrLBHC LLBcSTyGN6FsmuL9oJB7rKDt10q5XIIbsmdGsCilJ980M3RMKexbS+8K76d76BRrUsmxgqy6Bmq1jfibWoDUmODk4EiSmvVYWnRDbG9fn0DBHsYcgVYVLzDLpOXEH+Zkcq+3QQBUK3cNSyfFzKXq2xH7UA1yBJDoePwmqKw7ery1dyaHWpEgzbTgC7ZlXziNbFNMh36OCsixUolFmlcrGH7uHm8l+NUnnglxdQcFSYjSuy1H881Hrrv0RtNBcDGaQ2DSdVWADI6yZ+juIZ4ien7PZ4cXh5wLeCGwYkijGczjjAA7OHHjcy0D188eCepfE2lPSote3B1h2D9Y= 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: List-Subscribe: List-Unsubscribe: On Mon, Jul 07, 2025 at 11:06:25AM -0400, Liam R. Howlett wrote: > * Mike Rapoport [250707 07:32]: > > On Mon, Jul 07, 2025 at 01:11:02PM +0200, Peter Zijlstra wrote: > > > > > > err = __execmem_cache_free(&mas, ptr, GFP_KERNEL | __GFP_NORETRY); > > > if (err) { > > > mas_store_gfp(&mas, pending_free_set(ptr), GFP_KERNEL); > > > execmem_cache.pending_free_cnt++; > > > schedule_delayed_work(&execmem_cache_free_work, FREE_DELAY); > > > return true; > > > } > > > > > > schedule_work(&execmem_cache_clean_work); > > > return true; > > > } > > > > > > And now I have to ask what happens if mas_store_gfp() returns an error? > > > > AFAIU it won't. mas points to exact slot we've got the area from, nothing else > > can modify the tree because of the mutex, so that mas_store_gfp() > > essentially updates the value at an existing entry. > > > > I'll add a comment about it. > > > > Added @Liam to make sure I'm not saying nonsense :) > > > > Yes, if there is already a node with a value with the same range, there > will be no allocations that will happen, so it'll just change the > pointer for you. This is a slot store operation. > > But, if it's possible to have no entries (an empty tree, or a single > value at 0), you will most likely allocate a node to store it, which is > 256B. > > I don't think this is a concern in this particular case though as you > are searching for an entry and storing, so it needs to exist. So > really, the only scenario here is if you store 1 - ULONG_MAX (without > having expanded a root node) or 0 - ULONG_MAX, and that seems invalid. Thanks for clarification, Liam! The tree cannot be empty at that point and if it has a single value, it won't be at 0, I'm quite sure no architecture has execmem areas at 0. > Thanks, > Liam -- Sincerely yours, Mike.