The patch titled futex: runtime enable pi and robust functionality has been removed from the -mm tree. Its filename was futex-runtime-enable-pi-and-robust-functionality.patch This patch was dropped because it was merged into mainline or a subsystem tree The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: futex: runtime enable pi and robust functionality From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Not all architectures implement futex_atomic_cmpxchg_inatomic(). The default implementation returns -ENOSYS, which is currently not handled inside of the futex guts. Futex PI calls and robust list exits with a held futex result in an endless loop in the futex code on architectures which have no support. Fixing up every place where futex_atomic_cmpxchg_inatomic() is called would add a fair amount of extra if/else constructs to the already complex code. It is also not possible to disable the robust feature before user space tries to register robust lists. Compile time disabling is not a good idea either, as there are already architectures with runtime detection of futex_atomic_cmpxchg_inatomic support. Detect the functionality at runtime instead by calling cmpxchg_futex_value_locked() with a NULL pointer from the futex initialization code. This is guaranteed to fail, but the call of futex_atomic_cmpxchg_inatomic() happens with pagefaults disabled. On architectures, which use the asm-generic implementation or have a runtime CPU feature detection, a -ENOSYS return value disables the PI/robust features. On architectures with a working implementation the call returns -EFAULT and the PI/robust features are enabled. The relevant syscalls return -ENOSYS and the robust list exit code is blocked, when the detection fails. Fixes http://lkml.org/lkml/2008/2/11/149 Originally reported by: Lennart Buytenhek Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Acked-by: Ingo Molnar <mingo@xxxxxxx> Cc: Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx> Cc: Riku Voipio <riku.voipio@xxxxxxxxx> Cc: <stable@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/futex.h | 1 + kernel/futex.c | 38 ++++++++++++++++++++++++++++++++++---- kernel/futex_compat.c | 9 +++++++++ 3 files changed, 44 insertions(+), 4 deletions(-) diff -puN include/linux/futex.h~futex-runtime-enable-pi-and-robust-functionality include/linux/futex.h --- a/include/linux/futex.h~futex-runtime-enable-pi-and-robust-functionality +++ a/include/linux/futex.h @@ -167,6 +167,7 @@ union futex_key { #ifdef CONFIG_FUTEX extern void exit_robust_list(struct task_struct *curr); extern void exit_pi_state_list(struct task_struct *curr); +extern int futex_cmpxchg_enabled; #else static inline void exit_robust_list(struct task_struct *curr) { diff -puN kernel/futex.c~futex-runtime-enable-pi-and-robust-functionality kernel/futex.c --- a/kernel/futex.c~futex-runtime-enable-pi-and-robust-functionality +++ a/kernel/futex.c @@ -60,6 +60,8 @@ #include "rtmutex_common.h" +int __read_mostly futex_cmpxchg_enabled; + #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) /* @@ -469,6 +471,8 @@ void exit_pi_state_list(struct task_stru struct futex_hash_bucket *hb; union futex_key key; + if (!futex_cmpxchg_enabled) + return; /* * We are a ZOMBIE and nobody can enqueue itself on * pi_state_list anymore, but we have to be careful @@ -1870,6 +1874,8 @@ asmlinkage long sys_set_robust_list(struct robust_list_head __user *head, size_t len) { + if (!futex_cmpxchg_enabled) + return -ENOSYS; /* * The kernel knows only one size for now: */ @@ -1894,6 +1900,9 @@ sys_get_robust_list(int pid, struct robu struct robust_list_head __user *head; unsigned long ret; + if (!futex_cmpxchg_enabled) + return -ENOSYS; + if (!pid) head = current->robust_list; else { @@ -1997,6 +2006,9 @@ void exit_robust_list(struct task_struct unsigned long futex_offset; int rc; + if (!futex_cmpxchg_enabled) + return; + /* * Fetch the list head (which was registered earlier, via * sys_set_robust_list()): @@ -2051,7 +2063,7 @@ void exit_robust_list(struct task_struct long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, u32 __user *uaddr2, u32 val2, u32 val3) { - int ret; + int ret = -ENOSYS; int cmd = op & FUTEX_CMD_MASK; struct rw_semaphore *fshared = NULL; @@ -2083,13 +2095,16 @@ long do_futex(u32 __user *uaddr, int op, ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3); break; case FUTEX_LOCK_PI: - ret = futex_lock_pi(uaddr, fshared, val, timeout, 0); + if (futex_cmpxchg_enabled) + ret = futex_lock_pi(uaddr, fshared, val, timeout, 0); break; case FUTEX_UNLOCK_PI: - ret = futex_unlock_pi(uaddr, fshared); + if (futex_cmpxchg_enabled) + ret = futex_unlock_pi(uaddr, fshared); break; case FUTEX_TRYLOCK_PI: - ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1); + if (futex_cmpxchg_enabled) + ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1); break; default: ret = -ENOSYS; @@ -2145,8 +2160,23 @@ static struct file_system_type futex_fs_ static int __init init(void) { + u32 curval; int i; + /* + * This will fail and we want it. Some arch implementations do + * runtime detection of the futex_atomic_cmpxchg_inatomic() + * functionality. We want to know that before we call in any + * of the complex code paths. Also we want to prevent + * registration of robust lists in that case. NULL is + * guaranteed to fault and we get -EFAULT on functional + * implementation, the non functional ones will return + * -ENOSYS. + */ + curval = cmpxchg_futex_value_locked(NULL, 0, 0); + if (curval == -EFAULT) + futex_cmpxchg_enabled = 1; + for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock); spin_lock_init(&futex_queues[i].lock); diff -puN kernel/futex_compat.c~futex-runtime-enable-pi-and-robust-functionality kernel/futex_compat.c --- a/kernel/futex_compat.c~futex-runtime-enable-pi-and-robust-functionality +++ a/kernel/futex_compat.c @@ -54,6 +54,9 @@ void compat_exit_robust_list(struct task compat_long_t futex_offset; int rc; + if (!futex_cmpxchg_enabled) + return; + /* * Fetch the list head (which was registered earlier, via * sys_set_robust_list()): @@ -115,6 +118,9 @@ asmlinkage long compat_sys_set_robust_list(struct compat_robust_list_head __user *head, compat_size_t len) { + if (!futex_cmpxchg_enabled) + return -ENOSYS; + if (unlikely(len != sizeof(*head))) return -EINVAL; @@ -130,6 +136,9 @@ compat_sys_get_robust_list(int pid, comp struct compat_robust_list_head __user *head; unsigned long ret; + if (!futex_cmpxchg_enabled) + return -ENOSYS; + if (!pid) head = current->compat_robust_list; else { _ Patches currently in -mm which might be from tglx@xxxxxxxxxxxxx are git-hrt.patch git-kvm.patch execute-tasklets-in-the-same-order-they-were-queued.patch git-x86.patch documentation-i386-io-apictxt-fix-description.patch add-the-dff-desktop-form-factor-dell-optiplex-745-to-the-reboot-errata-list.patch x86-cast-cmpxchg-and-cmpxchg_local-result-for-386-and-486.patch x86-fix-clearcopy_user_page-declarations-in-pageh.patch x86-visws-fix-printk-format-warnings.patch fix-typo-in-tick-broadcastc.patch x86-configurable-dmi-scanning-code.patch kprobes-introduce-kprobe_handle_fault.patch kprobes-remove-preempt_enable-disable-from-kprobe_handle_fault.patch fix-shadowed-variables-in-kernel-posix-cpu-timersc.patch timers-simplify-lockdep-stuff.patch hrtimers-simplify-lockdep-stuff.patch kill-double_spin_lock.patch ntp-make-the-kernel-ntp-code-hand-64-bit-unsigned-values-to-do_div.patch asm-futexh-should-include-linux-uaccessh.patch init-move-setup-of-nr_cpu_ids-to-as-early-as-possible-v3.patch generic-percpu-infrastructure-to-rebase-the-per-cpu-area-to-zero-v3.patch x86_64-fold-pda-into-per-cpu-area-v3.patch x86_64-cleanup-non-smp-usage-of-cpu-maps-v3.patch - To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html