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Tue, 2 Apr 2024 06:54:28 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap2.dmz-prg2.suse.org with ESMTPSA id 0ry6F6SrC2YPQwAAn2gu4w (envelope-from ); Tue, 02 Apr 2024 06:54:28 +0000 Message-ID: Date: Tue, 2 Apr 2024 08:54:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] stackdepot: Rename pool_index to pool_index_plus_1 To: Peter Collingbourne , Andrey Konovalov , Oscar Salvador Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Marco Elver , Alexander Potapenko , Omar Sandoval References: <20240402001500.53533-1-pcc@google.com> Content-Language: en-US From: Vlastimil Babka In-Reply-To: <20240402001500.53533-1-pcc@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 4B45320015 X-Stat-Signature: 7jk838ksth3eiihf5eyg8qqwwi9z7wf7 X-Rspam-User: X-HE-Tag: 1712040870-112370 X-HE-Meta: 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 dPvfrPBF +i37vClMdAqBvO34XnY6xaYvdbpV5vha3gMScUAZ1llwqDRYdLlk+p7vT4rs8UMNU5WG9LclPM+xhd/1cAmtXI6b7qUECCMtMOQiT+kRl1kDV2pBQ7BuUZyNklL8NwPWaPanM6e50SrQ1RyFchwCBMcHtTCyTBYx5qofExy6zyJzzj+lhx+iZLlfwOSvSmWEivUykJY1W45hWLg8axchPifcTFBI3IlKDlJ9px3FCPwEAJ0JWviz81B0WpEYlRG5uLFQ4uQyFB3+5WX1K/iZxm9xNrMo/kRg/XQ+OfEW4wOeBr861MAh1lYu6/5IXR7sCalAu2Ky8ugs60aFFyzgOP/inmb1mvzFAsKL+D/4abOg1VX5YWINbdXFpsmnU9tSDiOqfoNh3ke0Lrh4= 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 4/2/24 2:14 AM, Peter Collingbourne wrote: > Commit 3ee34eabac2a ("lib/stackdepot: fix first entry having a > 0-handle") changed the meaning of the pool_index field to mean "the > pool index plus 1". This made the code accessing this field less > self-documenting, as well as causing debuggers such as drgn to not > be able to easily remain compatible with both old and new kernels, > because they typically do that by testing for presence of the new > field. Because stackdepot is a debugging tool, we should make sure > that it is debugger friendly. Therefore, give the field a different > name to improve readability as well as enabling debugger backwards > compatibility. > > Signed-off-by: Peter Collingbourne > Link: https://linux-review.googlesource.com/id/Ib3e70c36c1d230dd0a118dc22649b33e768b9f88 Acked-by: Vlastimil Babka > --- > Although this technically isn't a bug fix in the kernel, > I would appreciate if this could be picked up for 6.9 > to avoid temporarily introducing a silent regression in drgn > (loud regressions are fine). > > include/linux/stackdepot.h | 7 +++---- > lib/stackdepot.c | 4 ++-- > 2 files changed, 5 insertions(+), 6 deletions(-) > > diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h > index 3c6caa5abc7c..e9ec32fb97d4 100644 > --- a/include/linux/stackdepot.h > +++ b/include/linux/stackdepot.h > @@ -44,10 +44,9 @@ typedef u32 depot_stack_handle_t; > union handle_parts { > depot_stack_handle_t handle; > struct { > - /* pool_index is offset by 1 */ > - u32 pool_index : DEPOT_POOL_INDEX_BITS; > - u32 offset : DEPOT_OFFSET_BITS; > - u32 extra : STACK_DEPOT_EXTRA_BITS; > + u32 pool_index_plus_1 : DEPOT_POOL_INDEX_BITS; > + u32 offset : DEPOT_OFFSET_BITS; > + u32 extra : STACK_DEPOT_EXTRA_BITS; > }; > }; > > diff --git a/lib/stackdepot.c b/lib/stackdepot.c > index af6cc19a2003..68c97387aa54 100644 > --- a/lib/stackdepot.c > +++ b/lib/stackdepot.c > @@ -330,7 +330,7 @@ static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size) > stack = current_pool + pool_offset; > > /* Pre-initialize handle once. */ > - stack->handle.pool_index = pool_index + 1; > + stack->handle.pool_index_plus_1 = pool_index + 1; > stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN; > stack->handle.extra = 0; > INIT_LIST_HEAD(&stack->hash_list); > @@ -441,7 +441,7 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle) > const int pools_num_cached = READ_ONCE(pools_num); > union handle_parts parts = { .handle = handle }; > void *pool; > - u32 pool_index = parts.pool_index - 1; > + u32 pool_index = parts.pool_index_plus_1 - 1; > size_t offset = parts.offset << DEPOT_STACK_ALIGN; > struct stack_record *stack; >