It is common for services to be stateless around their main event loop. If a process passes the EPOLL_KILLME flag to epoll_wait5() then it signals to the kernel that epoll_wait5() may not complete, and the kernel may send SIGKILL if resources get tight.
See my systemd patch: https://github.com/shawnl/systemd/tree/killme Android uses this memory model for all programs, and having it in the kernel will enable integration with the page cache (not in this series). --- arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + fs/eventpoll.c | 74 +++++++++++++++++++++++++++++++++- include/linux/eventpoll.h | 2 + include/linux/sched.h | 3 ++ include/uapi/asm-generic/unistd.h | 5 ++- include/uapi/linux/eventpoll.h | 3 ++ kernel/exit.c | 2 + mm/oom_kill.c | 17 ++++++++ 9 files changed, 105 insertions(+), 3 deletions(-) diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 448ac2161112..040e5d02bdcc 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -391,3 +391,4 @@ 382 i386 pkey_free sys_pkey_free 383 i386 statx sys_statx 384 i386 arch_prctl sys_arch_prctl compat_sys_arch_prctl +385 i386 epoll_wait5 sys_epoll_wait5 diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index 5aef183e2f85..c72802e8cf65 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -339,6 +339,7 @@ 330 common pkey_alloc sys_pkey_alloc 331 common pkey_free sys_pkey_free 332 common statx sys_statx +333 common epoll_wait5 sys_epoll_wait5 # # x32-specific system call numbers start at 512 to avoid cache impact diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 2fabd19cdeea..76d1c91d940b 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -297,6 +297,14 @@ static LIST_HEAD(visited_list); */ static LIST_HEAD(tfile_check_list); +static LIST_HEAD(deathrow_q); +static long deathrow_len __read_mostly; + +/* TODO: Can this lock be removed by using atomic instructions to update + * queue? + */ +static DEFINE_MUTEX(deathrow_mutex); + #ifdef CONFIG_SYSCTL #include <linux/sysctl.h> @@ -314,6 +322,15 @@ struct ctl_table epoll_table[] = { .extra1 = &zero, .extra2 = &long_max, }, + { + .procname = "deathrow_size", + .data = &deathrow_len, + .maxlen = sizeof(deathrow_len), + .mode = 0444, + .proc_handler = proc_doulongvec_minmax, + .extra1 = &zero, + .extra2 = &long_max, + }, { } }; #endif /* CONFIG_SYSCTL */ @@ -2164,9 +2181,12 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, /* * Implement the event wait interface for the eventpoll file. It is the kernel * part of the user space epoll_wait(2). + * + * A flags argument cannot be added to epoll_pwait cause it already has + * the maximum number of arguments (6). Can this be fixed? */ -SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, - int, maxevents, int, timeout) +SYSCALL_DEFINE5(epoll_wait5, int, epfd, struct epoll_event __user *, events, + int, maxevents, int, timeout, int, flags) { int error; struct fd f; @@ -2199,14 +2219,44 @@ SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, */ ep = f.file->private_data; + /* Check the EPOLL_* constants for conflicts. */ + BUILD_BUG_ON(EPOLL_KILLME == EPOLL_CLOEXEC); + + if (flags & ~EPOLL_KILLME) + return -EINVAL; + + if (flags & EPOLL_KILLME) { + /* Put process on death row. */ + mutex_lock(&deathrow_mutex); + deathrow_len++; + list_add(¤t->se.deathrow, &deathrow_q); + current->se.on_deathrow = 1; + mutex_unlock(&deathrow_mutex); + } + /* Time to fish for events ... */ error = ep_poll(ep, events, maxevents, timeout); + if (flags & EPOLL_KILLME) { + /* Remove process from death row. */ + mutex_lock(&deathrow_mutex); + current->se.on_deathrow = 0; + list_del(¤t->se.deathrow); + deathrow_len--; + mutex_unlock(&deathrow_mutex); + } + error_fput: fdput(f); return error; } +SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, + int, maxevents, int, timeout) +{ + return sys_epoll_wait5(epfd, events, maxevents, timeout, 0); +} + /* * Implement the event wait interface for the eventpoll file. It is the kernel * part of the user space epoll_pwait(2). @@ -2297,6 +2347,26 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd, } #endif +/* Clean up after a EPOLL_KILLME process quits. + * Called by kernel/exit.c. + */ +int exit_killme(void) +{ + if (current->se.on_deathrow) { + mutex_lock(&deathrow_mutex); + current->se.on_deathrow = 0; + list_del(¤t->se.deathrow); + mutex_unlock(&deathrow_mutex); + } + + return 0; +} + +struct list_head *eventpoll_deathrow_list(void) +{ + return &deathrow_q; +} + static int __init eventpoll_init(void) { struct sysinfo si; diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h index 2f14ac73d01d..f1e28d468de5 100644 --- a/include/linux/eventpoll.h +++ b/include/linux/eventpoll.h @@ -20,6 +20,8 @@ /* Forward declarations to avoid compiler errors */ struct file; +int exit_killme(void); +struct list_head *eventpoll_deathrow_list(void); #ifdef CONFIG_EPOLL diff --git a/include/linux/sched.h b/include/linux/sched.h index 26a7df4e558c..66462bf27a29 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -380,6 +380,9 @@ struct sched_entity { struct list_head group_node; unsigned int on_rq; + unsigned on_deathrow:1; + struct list_head deathrow; + u64 exec_start; u64 sum_exec_runtime; u64 vruntime; diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 061185a5eb51..843553a39388 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -893,8 +893,11 @@ __SYSCALL(__NR_fork, sys_fork) __SYSCALL(__NR_fork, sys_ni_syscall) #endif /* CONFIG_MMU */ +#define __NR_epoll_wait5 1080 +__SYSCALL(__NR_epoll_wait5, sys_epoll_wait5) + #undef __NR_syscalls -#define __NR_syscalls (__NR_fork+1) +#define __NR_syscalls (__NR_fork+2) #endif /* __ARCH_WANT_SYSCALL_DEPRECATED */ diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h index f4d5c998cc2b..ce150a3e7248 100644 --- a/include/uapi/linux/eventpoll.h +++ b/include/uapi/linux/eventpoll.h @@ -21,6 +21,9 @@ /* Flags for epoll_create1. */ #define EPOLL_CLOEXEC O_CLOEXEC +/* Flags for epoll_wait5. */ +#define EPOLL_KILLME 0x00000001 + /* Valid opcodes to issue to sys_epoll_ctl() */ #define EPOLL_CTL_ADD 1 #define EPOLL_CTL_DEL 2 diff --git a/kernel/exit.c b/kernel/exit.c index f6cad39f35df..cd089bdc5b17 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -62,6 +62,7 @@ #include <linux/random.h> #include <linux/rcuwait.h> #include <linux/compat.h> +#include <linux/eventpoll.h> #include <linux/uaccess.h> #include <asm/unistd.h> @@ -917,6 +918,7 @@ void __noreturn do_exit(long code) __this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied); exit_rcu(); exit_tasks_rcu_finish(); + exit_killme(); lockdep_free_task(tsk); do_task_dead(); diff --git a/mm/oom_kill.c b/mm/oom_kill.c index dee0f75c3013..d6252772d593 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -41,6 +41,7 @@ #include <linux/kthread.h> #include <linux/init.h> #include <linux/mmu_notifier.h> +#include <linux/eventpoll.h> #include <asm/tlb.h> #include "internal.h" @@ -1029,6 +1030,22 @@ bool out_of_memory(struct oom_control *oc) return true; } + /* + * Check death row. + */ + if (!list_empty(eventpoll_deathrow_list())) { + struct list_head *l = eventpoll_deathrow_list(); + struct task_struct *ts = list_first_entry(l, + struct task_struct, se.deathrow); + + pr_debug("Killing pid %u from EPOLL_KILLME death row.", + ts->pid); + + /* We use SIGKILL so as to cleanly interrupt ep_poll() */ + kill_pid(task_pid(ts), SIGKILL, 1); + return true; + } + /* * The OOM killer does not compensate for IO-less reclaim. * pagefault_out_of_memory lost its gfp context so we have to -- 2.15.0.rc2
