From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ECF663C3C01 for ; Thu, 2 Apr 2026 15:21:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775143285; cv=none; b=mgMCMt4dbuq5Bryjx8pVFeGX7Q90EBmyG5Z2Kuuj1PtF9PZ8D35cA13OBQKqVVSrkS3omRy2ZUfnpay6+JnEwPPVJMVkSJIyUeo1Zt3gMW8Vii0E9817UEVZQVK+s88Yl/GyFcpXhb36OnAgVctD4fK3DPFQyHKzKpp2cuezsS4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775143285; c=relaxed/simple; bh=0UKyLgi+QXlQYcXNJ1q8D0LWspVCBBnXm3UroC4BxaM=; h=Date:Message-ID:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=g/JV7YA4WZ9bSA0BgwbWYaxhZNZVktcKaM08N4a20wj+aIBGTBh493iWs1W2l2lnyetcLJ316Q7fqK30Rk7XZShrDRbP2GNY0ISpCm+5qejuaeJGilTHFB7mp5ivAXGFGfL0lEYPz1D1I0krb3lWn+rqfG0u8Trhznv+nBxuiwU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OqQHFcXK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OqQHFcXK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0A547C116C6; Thu, 2 Apr 2026 15:21:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775143284; bh=0UKyLgi+QXlQYcXNJ1q8D0LWspVCBBnXm3UroC4BxaM=; h=Date:From:To:Cc:Subject:References:From; b=OqQHFcXKKWRomXTJQoEM2jEFFv2n1VZXEXAGl4bzn/O7OrUhpuoB8sxgkXnAWD3Hw 6vl4ERxOOMi7lYUMgz2f7PI5MVtsP3YVXq7bw6Xwy1t/SVBxx3ynK8SARM+BDdrr2E TgSQArv7trcWJUhESvV2ZEyZIox37d1ZzSSTHp8doBhUmrtNgsyqSbjXu1panNds+v gWrHx4ftP1j4IwOtJQxjWGToKUu3JCt1JHVsYZV4NWHuoKP/hEF3DTnLwInFl9cFgJ O51su/hFFXUpcknpLp15iK0hmNOcrCqSeV3ZFcUYlOhGouL8xutBiQE8d1D9GonMDG bqhlk+f3iYS0Q== Date: Thu, 02 Apr 2026 17:21:21 +0200 Message-ID: <20260402151939.867541565@kernel.org> User-Agent: quilt/0.68 From: Thomas Gleixner To: LKML Cc: Mathieu Desnoyers , =?UTF-8?q?Andr=C3=A8=20Almeida?= , Sebastian Andrzej Siewior , Carlos O'Donell , Peter Zijlstra , Florian Weimer , Rich Felker , Torvald Riegel , Darren Hart , Ingo Molnar , Davidlohr Bueso , Arnd Bergmann , "Liam R . Howlett" , Uros Bizjak , =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= Subject: [patch V4 04/14] futex: Provide UABI defines for robust list entry modifiers References: <20260402151131.876492985@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 The marker for PI futexes in the robust list is a hardcoded 0x1 which lacks any sensible form of documentation. Provide proper defines for the bit and the mask and fix up the usage sites. Thereby convert the boolean pi argument into a modifier argument, which allows new modifier bits to be trivially added and conveyed. Signed-off-by: Thomas Gleixner Reviewed-by: Mathieu Desnoyers Reviewed-by: André Almeida --- V2: Explain the code shuffling - Andre --- include/uapi/linux/futex.h | 4 +++ kernel/futex/core.c | 53 +++++++++++++++++++++------------------------ 2 files changed, 29 insertions(+), 28 deletions(-) --- a/include/uapi/linux/futex.h +++ b/include/uapi/linux/futex.h @@ -177,6 +177,10 @@ struct robust_list_head { */ #define ROBUST_LIST_LIMIT 2048 +/* Modifiers for robust_list_head::list_op_pending */ +#define FUTEX_ROBUST_MOD_PI (0x1UL) +#define FUTEX_ROBUST_MOD_MASK (FUTEX_ROBUST_MOD_PI) + /* * bitset with all bits set for the FUTEX_xxx_BITSET OPs to request a * match of any bit. --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -1009,8 +1009,9 @@ void futex_unqueue_pi(struct futex_q *q) * dying task, and do notification if so: */ static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, - bool pi, bool pending_op) + unsigned int mod, bool pending_op) { + bool pi = !!(mod & FUTEX_ROBUST_MOD_PI); u32 uval, nval, mval; pid_t owner; int err; @@ -1128,21 +1129,21 @@ static int handle_futex_death(u32 __user */ static inline int fetch_robust_entry(struct robust_list __user **entry, struct robust_list __user * __user *head, - unsigned int *pi) + unsigned int *mod) { unsigned long uentry; if (get_user(uentry, (unsigned long __user *)head)) return -EFAULT; - *entry = (void __user *)(uentry & ~1UL); - *pi = uentry & 1; + *entry = (void __user *)(uentry & ~FUTEX_ROBUST_MOD_MASK); + *mod = uentry & FUTEX_ROBUST_MOD_MASK; return 0; } /* - * Walk curr->robust_list (very carefully, it's a userspace list!) + * Walk curr->futex.robust_list (very carefully, it's a userspace list!) * and mark any locks found there dead, and notify any waiters. * * We silently return on any sign of list-walking problem. @@ -1150,9 +1151,8 @@ static inline int fetch_robust_entry(str static void exit_robust_list(struct task_struct *curr) { struct robust_list_head __user *head = curr->futex.robust_list; + unsigned int limit = ROBUST_LIST_LIMIT, cur_mod, next_mod, pend_mod; struct robust_list __user *entry, *next_entry, *pending; - unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; - unsigned int next_pi; unsigned long futex_offset; int rc; @@ -1160,7 +1160,7 @@ static void exit_robust_list(struct task * Fetch the list head (which was registered earlier, via * sys_set_robust_list()): */ - if (fetch_robust_entry(&entry, &head->list.next, &pi)) + if (fetch_robust_entry(&entry, &head->list.next, &cur_mod)) return; /* * Fetch the relative futex offset: @@ -1171,7 +1171,7 @@ static void exit_robust_list(struct task * Fetch any possibly pending lock-add first, and handle it * if it exists: */ - if (fetch_robust_entry(&pending, &head->list_op_pending, &pip)) + if (fetch_robust_entry(&pending, &head->list_op_pending, &pend_mod)) return; next_entry = NULL; /* avoid warning with gcc */ @@ -1180,20 +1180,20 @@ static void exit_robust_list(struct task * Fetch the next entry in the list before calling * handle_futex_death: */ - rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi); + rc = fetch_robust_entry(&next_entry, &entry->next, &next_mod); /* * A pending lock might already be on the list, so * don't process it twice: */ if (entry != pending) { if (handle_futex_death((void __user *)entry + futex_offset, - curr, pi, HANDLE_DEATH_LIST)) + curr, cur_mod, HANDLE_DEATH_LIST)) return; } if (rc) return; entry = next_entry; - pi = next_pi; + cur_mod = next_mod; /* * Avoid excessively long or circular lists: */ @@ -1205,7 +1205,7 @@ static void exit_robust_list(struct task if (pending) { handle_futex_death((void __user *)pending + futex_offset, - curr, pip, HANDLE_DEATH_PENDING); + curr, pend_mod, HANDLE_DEATH_PENDING); } } @@ -1224,29 +1224,28 @@ static void __user *futex_uaddr(struct r */ static inline int compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry, - compat_uptr_t __user *head, unsigned int *pi) + compat_uptr_t __user *head, unsigned int *pflags) { if (get_user(*uentry, head)) return -EFAULT; - *entry = compat_ptr((*uentry) & ~1); - *pi = (unsigned int)(*uentry) & 1; + *entry = compat_ptr((*uentry) & ~FUTEX_ROBUST_MOD_MASK); + *pflags = (unsigned int)(*uentry) & FUTEX_ROBUST_MOD_MASK; return 0; } /* - * Walk curr->robust_list (very carefully, it's a userspace list!) + * Walk curr->futex.robust_list (very carefully, it's a userspace list!) * and mark any locks found there dead, and notify any waiters. * * We silently return on any sign of list-walking problem. */ static void compat_exit_robust_list(struct task_struct *curr) { - struct compat_robust_list_head __user *head = curr->futex.compat_robust_list; + struct compat_robust_list_head __user *head = current->futex.compat_robust_list; + unsigned int limit = ROBUST_LIST_LIMIT, cur_mod, next_mod, pend_mod; struct robust_list __user *entry, *next_entry, *pending; - unsigned int limit = ROBUST_LIST_LIMIT, pi, pip; - unsigned int next_pi; compat_uptr_t uentry, next_uentry, upending; compat_long_t futex_offset; int rc; @@ -1255,7 +1254,7 @@ static void compat_exit_robust_list(stru * Fetch the list head (which was registered earlier, via * sys_set_robust_list()): */ - if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi)) + if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &cur_mod)) return; /* * Fetch the relative futex offset: @@ -1266,8 +1265,7 @@ static void compat_exit_robust_list(stru * Fetch any possibly pending lock-add first, and handle it * if it exists: */ - if (compat_fetch_robust_entry(&upending, &pending, - &head->list_op_pending, &pip)) + if (compat_fetch_robust_entry(&upending, &pending, &head->list_op_pending, &pend_mod)) return; next_entry = NULL; /* avoid warning with gcc */ @@ -1277,7 +1275,7 @@ static void compat_exit_robust_list(stru * handle_futex_death: */ rc = compat_fetch_robust_entry(&next_uentry, &next_entry, - (compat_uptr_t __user *)&entry->next, &next_pi); + (compat_uptr_t __user *)&entry->next, &next_mod); /* * A pending lock might already be on the list, so * dont process it twice: @@ -1285,15 +1283,14 @@ static void compat_exit_robust_list(stru if (entry != pending) { void __user *uaddr = futex_uaddr(entry, futex_offset); - if (handle_futex_death(uaddr, curr, pi, - HANDLE_DEATH_LIST)) + if (handle_futex_death(uaddr, curr, cur_mod, HANDLE_DEATH_LIST)) return; } if (rc) return; uentry = next_uentry; entry = next_entry; - pi = next_pi; + cur_mod = next_mod; /* * Avoid excessively long or circular lists: */ @@ -1305,7 +1302,7 @@ static void compat_exit_robust_list(stru if (pending) { void __user *uaddr = futex_uaddr(pending, futex_offset); - handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING); + handle_futex_death(uaddr, curr, pend_mod, HANDLE_DEATH_PENDING); } } #endif