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Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH] selftests/mm: Fix thread state check in uffd-unit-tests Message-ID: References: <20251210091408.3781445-1-wakel@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251210091408.3781445-1-wakel@google.com> X-Rspam-User: X-Rspamd-Queue-Id: 932C84000C X-Rspamd-Server: rspam10 X-Stat-Signature: 5xodx3dfnyx5cs7uycjf7uxd96k436ri X-HE-Tag: 1765865742-554058 X-HE-Meta: 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 Hv0m0O7R cJKTK0UX1pCCrTy5wr6FsyqBOWBUIdRDKrVSWDUfPzu5iBzWSgOIghVhFXOuXl4ahkvvZpDLdiLQ27rfxDMSbvfEbudm7CtvkWiGE0FvlLnbehAeDoSNt8MR+mt/bQQxxo6U/tvlPM02o8zvZcZ2/IEatwz0YhLOi84f2wzfDC+RRnQU5W4dzPe+a7uqhbv2UaiDVwI4KYhIb9Kwb0ndgiUDNdMLEVA24awhieBzv2vbpJeZ98tG7SoEpg65f5pEOUaT9gqcd54Z3POEb7QzDSimYyofr3HfJsSOeoCFg5vTYw1iOkgJi1HRnVnzcEPz8wJgdaThE847ssZN+akUUaIMCW9yKHNbyFC6yX1fvfu9BUJkR0CmRiwCVjllgRTf11tIR 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 Wed, Dec 10, 2025 at 05:14:08PM +0800, Wake Liu wrote: > In the thread_state_get() function, the logic to find the thread's state > character was using `sizeof(header) - 1` to calculate the offset from > the "State:\t" string. > > The `header` variable is a `const char *` pointer. `sizeof()` on a > pointer returns the size of the pointer itself, not the length of the > string literal it points to. This makes the code's behavior dependent > on the architecture's pointer size. > > This bug was identified on a 32-bit ARM build (`gsi_tv_arm`) for > Android, running on an ARMv8-based device, compiled with Clang 19.0.1. > > On this 32-bit architecture, `sizeof(char *)` is 4. The expression > `sizeof(header) - 1` resulted in an incorrect offset of 3, causing the > test to read the wrong character from `/proc/[tid]/status` and fail. > > On 64-bit architectures, `sizeof(char *)` is 8, so the expression > coincidentally evaluates to 7, which matches the length of "State:\t". > This is why the bug likely remained hidden on 64-bit builds. > > To fix this and make the code portable and correct across all > architectures, this patch replaces `sizeof(header) - 1` with > `strlen(header)`. The `strlen()` function correctly calculates the > string's length, ensuring the correct offset is always used. > > Signed-off-by: Wake Liu Reviewed-by: Mike Rapoport (Microsoft) > --- > tools/testing/selftests/mm/uffd-unit-tests.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c > index f4807242c5b2..6f5e404a446c 100644 > --- a/tools/testing/selftests/mm/uffd-unit-tests.c > +++ b/tools/testing/selftests/mm/uffd-unit-tests.c > @@ -1317,7 +1317,7 @@ static thread_state thread_state_get(pid_t tid) > p = strstr(tmp, header); > if (p) { > /* For example, "State:\tD (disk sleep)" */ > - c = *(p + sizeof(header) - 1); > + c = *(p + strlen(header)); > return c == 'D' ? > THR_STATE_UNINTERRUPTIBLE : THR_STATE_UNKNOWN; > } > -- > 2.52.0.223.gf5cc29aaa4-goog > -- Sincerely yours, Mike.