Manage process-related IDs with bitmaps
Currently unique pid allocation on fork often requires a full walk of process, group, session lists to make sure it is not used by anything. This has a side effect of requiring proctree to be held along with allproc, which adds more contention in poudriere -j 128. The patch below implements trivial bitmaps which gets rid of the problem. Dedicated lock is introduced to manage IDs. While here a bug was discovered: all processes would inherit reap id from the first process spawned by init. This had a side effect of keeping the ID used and when allocation rolls over to the beginning it keeps being skipped. The patch is loosely based on initial work by mjoras@. Reviewed by: kib Sponsored by: The FreeBSD Foundation
This commit is contained in:
Mateusz Guzik
parent
6e8c1ccbe2
commit
34ebdceac0
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=341684
@ -147,6 +147,27 @@ reaper_abandon_children(struct proc *p, bool exiting)
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p->p_treeflag &= ~P_TREE_REAPER;
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}
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static void
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reaper_clear(struct proc *p)
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{
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struct proc *p1;
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bool clear;
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sx_assert(&proctree_lock, SX_LOCKED);
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LIST_REMOVE(p, p_reapsibling);
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if (p->p_reapsubtree == 1)
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return;
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clear = true;
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LIST_FOREACH(p1, &p->p_reaper->p_reaplist, p_reapsibling) {
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if (p1->p_reapsubtree == p->p_reapsubtree) {
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clear = false;
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break;
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}
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}
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if (clear)
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proc_id_clear(PROC_ID_REAP, p->p_reapsubtree);
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}
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static void
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clear_orphan(struct proc *p)
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{
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@ -881,7 +902,8 @@ proc_reap(struct thread *td, struct proc *p, int *status, int options)
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sx_xunlock(PIDHASHLOCK(p->p_pid));
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LIST_REMOVE(p, p_sibling);
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reaper_abandon_children(p, true);
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LIST_REMOVE(p, p_reapsibling);
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reaper_clear(p);
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proc_id_clear(PROC_ID_PID, p->p_pid);
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PROC_LOCK(p);
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clear_orphan(p);
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PROC_UNLOCK(p);
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@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/bitstring.h>
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#include <sys/sysproto.h>
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#include <sys/eventhandler.h>
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#include <sys/fcntl.h>
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@ -232,20 +233,16 @@ sysctl_kern_randompid(SYSCTL_HANDLER_ARGS)
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SYSCTL_PROC(_kern, OID_AUTO, randompid, CTLTYPE_INT|CTLFLAG_RW,
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0, 0, sysctl_kern_randompid, "I", "Random PID modulus. Special values: 0: disable, 1: choose random value");
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extern bitstr_t proc_id_pidmap;
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extern bitstr_t proc_id_grpidmap;
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extern bitstr_t proc_id_sessidmap;
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extern bitstr_t proc_id_reapmap;
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static int
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fork_findpid(int flags)
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{
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struct proc *p;
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pid_t result;
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int trypid;
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static int pidchecked = 0;
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bool locked_zomb = false;
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/*
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* Requires allproc_lock in order to iterate over the list
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* of processes, and proctree_lock to access p_pgrp.
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*/
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sx_assert(&allproc_lock, SX_LOCKED);
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sx_assert(&proctree_lock, SX_LOCKED);
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/*
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* Find an unused process ID. We remember a range of unused IDs
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@ -262,6 +259,7 @@ fork_findpid(int flags)
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if (randompid)
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trypid += arc4random() % randompid;
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}
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mtx_lock(&procid_lock);
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retry:
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/*
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* If the process ID prototype has wrapped around,
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@ -272,74 +270,28 @@ fork_findpid(int flags)
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trypid = trypid % pid_max;
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if (trypid < 100)
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trypid += 100;
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pidchecked = 0;
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}
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if (trypid >= pidchecked) {
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int doingzomb = 0;
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pidchecked = PID_MAX;
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/*
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* Scan the active and zombie procs to check whether this pid
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* is in use. Remember the lowest pid that's greater
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* than trypid, so we can avoid checking for a while.
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*
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* Avoid reuse of the process group id, session id or
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* the reaper subtree id. Note that for process group
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* and sessions, the amount of reserved pids is
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* limited by process limit. For the subtree ids, the
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* id is kept reserved only while there is a
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* non-reaped process in the subtree, so amount of
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* reserved pids is limited by process limit times
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* two.
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*/
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p = LIST_FIRST(&allproc);
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again:
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for (; p != NULL; p = LIST_NEXT(p, p_list)) {
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while (p->p_pid == trypid ||
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p->p_reapsubtree == trypid ||
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(p->p_pgrp != NULL &&
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(p->p_pgrp->pg_id == trypid ||
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(p->p_session != NULL &&
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p->p_session->s_sid == trypid)))) {
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trypid++;
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if (trypid >= pidchecked)
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goto retry;
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}
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if (p->p_pid > trypid && pidchecked > p->p_pid)
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pidchecked = p->p_pid;
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if (p->p_pgrp != NULL) {
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if (p->p_pgrp->pg_id > trypid &&
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pidchecked > p->p_pgrp->pg_id)
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pidchecked = p->p_pgrp->pg_id;
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if (p->p_session != NULL &&
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p->p_session->s_sid > trypid &&
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pidchecked > p->p_session->s_sid)
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pidchecked = p->p_session->s_sid;
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}
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}
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if (!doingzomb) {
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doingzomb = 1;
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if (!locked_zomb) {
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sx_slock(&zombproc_lock);
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locked_zomb = true;
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}
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p = LIST_FIRST(&zombproc);
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goto again;
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}
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bit_ffc_at(&proc_id_pidmap, trypid, pid_max, &result);
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if (result == -1)
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goto retry;
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if (bit_test(&proc_id_grpidmap, result) ||
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bit_test(&proc_id_sessidmap, result) ||
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bit_test(&proc_id_reapmap, result)) {
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trypid++;
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goto retry;
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}
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/*
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* RFHIGHPID does not mess with the lastpid counter during boot.
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*/
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if (flags & RFHIGHPID)
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pidchecked = 0;
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else
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lastpid = trypid;
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if ((flags & RFHIGHPID) == 0)
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lastpid = result;
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if (locked_zomb)
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sx_sunlock(&zombproc_lock);
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bit_set(&proc_id_pidmap, result);
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mtx_unlock(&procid_lock);
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return (trypid);
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return (result);
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}
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static int
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@ -402,13 +354,11 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *
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struct filedesc_to_leader *fdtol;
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struct sigacts *newsigacts;
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sx_assert(&proctree_lock, SX_LOCKED);
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sx_assert(&allproc_lock, SX_XLOCKED);
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p1 = td->td_proc;
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trypid = fork_findpid(fr->fr_flags);
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p2->p_state = PRS_NEW; /* protect against others */
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p2->p_pid = trypid;
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AUDIT_ARG_PID(p2->p_pid);
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@ -421,7 +371,6 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *
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PROC_LOCK(p1);
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sx_xunlock(&allproc_lock);
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sx_xunlock(&proctree_lock);
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bcopy(&p1->p_startcopy, &p2->p_startcopy,
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__rangeof(struct proc, p_startcopy, p_endcopy));
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@ -657,8 +606,10 @@ do_fork(struct thread *td, struct fork_req *fr, struct proc *p2, struct thread *
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LIST_INSERT_HEAD(&pptr->p_children, p2, p_sibling);
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LIST_INIT(&p2->p_reaplist);
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LIST_INSERT_HEAD(&p2->p_reaper->p_reaplist, p2, p_reapsibling);
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if (p2->p_reaper == p1)
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if (p2->p_reaper == p1 && p1 != initproc) {
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p2->p_reapsubtree = p2->p_pid;
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proc_id_set_cond(PROC_ID_REAP, p2->p_pid);
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}
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sx_xunlock(&proctree_lock);
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/* Inform accounting that we have forked. */
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@ -975,8 +926,6 @@ fork1(struct thread *td, struct fork_req *fr)
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newproc->p_klist = knlist_alloc(&newproc->p_mtx);
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STAILQ_INIT(&newproc->p_ktr);
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/* We have to lock the process tree while we look for a pid. */
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sx_xlock(&proctree_lock);
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sx_xlock(&allproc_lock);
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/*
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@ -999,7 +948,6 @@ fork1(struct thread *td, struct fork_req *fr)
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error = EAGAIN;
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sx_xunlock(&allproc_lock);
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sx_xunlock(&proctree_lock);
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#ifdef MAC
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mac_proc_destroy(newproc);
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#endif
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@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/bitstring.h>
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#include <sys/elf.h>
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#include <sys/eventhandler.h>
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#include <sys/exec.h>
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@ -128,6 +129,7 @@ struct sx __exclusive_cache_line allproc_lock;
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struct sx __exclusive_cache_line zombproc_lock;
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struct sx __exclusive_cache_line proctree_lock;
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struct mtx __exclusive_cache_line ppeers_lock;
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struct mtx __exclusive_cache_line procid_lock;
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uma_zone_t proc_zone;
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/*
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@ -181,6 +183,7 @@ procinit(void)
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sx_init(&zombproc_lock, "zombproc");
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sx_init(&proctree_lock, "proctree");
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mtx_init(&ppeers_lock, "p_peers", NULL, MTX_DEF);
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mtx_init(&procid_lock, "procid", NULL, MTX_DEF);
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LIST_INIT(&allproc);
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LIST_INIT(&zombproc);
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pidhashtbl = hashinit(maxproc / 4, M_PROC, &pidhash);
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@ -292,6 +295,62 @@ proc_fini(void *mem, int size)
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#endif
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}
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/*
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* PID space management.
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*
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* These bitmaps are used by fork_findpid.
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*/
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bitstr_t bit_decl(proc_id_pidmap, PID_MAX);
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bitstr_t bit_decl(proc_id_grpidmap, PID_MAX);
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bitstr_t bit_decl(proc_id_sessidmap, PID_MAX);
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bitstr_t bit_decl(proc_id_reapmap, PID_MAX);
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static bitstr_t *proc_id_array[] = {
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proc_id_pidmap,
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proc_id_grpidmap,
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proc_id_sessidmap,
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proc_id_reapmap,
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};
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void
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proc_id_set(int type, pid_t id)
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{
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KASSERT(type >= 0 && type < nitems(proc_id_array),
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("invalid type %d\n", type));
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mtx_lock(&procid_lock);
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KASSERT(bit_test(proc_id_array[type], id) == 0,
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("bit %d already set in %d\n", id, type));
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bit_set(proc_id_array[type], id);
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mtx_unlock(&procid_lock);
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}
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void
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proc_id_set_cond(int type, pid_t id)
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{
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KASSERT(type >= 0 && type < nitems(proc_id_array),
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("invalid type %d\n", type));
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if (bit_test(proc_id_array[type], id))
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return;
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mtx_lock(&procid_lock);
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bit_set(proc_id_array[type], id);
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mtx_unlock(&procid_lock);
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}
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void
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proc_id_clear(int type, pid_t id)
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{
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KASSERT(type >= 0 && type < nitems(proc_id_array),
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("invalid type %d\n", type));
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mtx_lock(&procid_lock);
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KASSERT(bit_test(proc_id_array[type], id) != 0,
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("bit %d not set in %d\n", id, type));
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bit_clear(proc_id_array[type], id);
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mtx_unlock(&procid_lock);
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}
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/*
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* Is p an inferior of the current process?
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*/
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@ -495,6 +554,7 @@ enterpgrp(struct proc *p, pid_t pgid, struct pgrp *pgrp, struct session *sess)
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PGRP_LOCK(pgrp);
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sess->s_leader = p;
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sess->s_sid = p->p_pid;
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proc_id_set(PROC_ID_SESSION, p->p_pid);
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refcount_init(&sess->s_count, 1);
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sess->s_ttyvp = NULL;
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sess->s_ttydp = NULL;
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@ -510,6 +570,7 @@ enterpgrp(struct proc *p, pid_t pgid, struct pgrp *pgrp, struct session *sess)
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PGRP_LOCK(pgrp);
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}
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pgrp->pg_id = pgid;
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proc_id_set(PROC_ID_GROUP, p->p_pid);
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LIST_INIT(&pgrp->pg_members);
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/*
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@ -640,6 +701,7 @@ pgdelete(struct pgrp *pgrp)
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tty_rel_pgrp(tp, pgrp);
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}
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proc_id_clear(PROC_ID_GROUP, pgrp->pg_id);
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mtx_destroy(&pgrp->pg_mtx);
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free(pgrp, M_PGRP);
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sess_release(savesess);
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@ -824,6 +886,7 @@ sess_release(struct session *s)
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tty_lock(s->s_ttyp);
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tty_rel_sess(s->s_ttyp, s);
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}
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proc_id_clear(PROC_ID_SESSION, s->s_sid);
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mtx_destroy(&s->s_mtx);
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free(s, M_SESSION);
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}
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@ -962,6 +962,7 @@ extern int allproc_gen;
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extern struct sx zombproc_lock;
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extern struct sx proctree_lock;
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extern struct mtx ppeers_lock;
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extern struct mtx procid_lock;
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extern struct proc proc0; /* Process slot for swapper. */
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extern struct thread0_storage thread0_st; /* Primary thread in proc0. */
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#define thread0 (thread0_st.t0st_thread)
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@ -1165,6 +1166,15 @@ td_softdep_cleanup(struct thread *td)
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softdep_ast_cleanup(td);
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}
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#define PROC_ID_PID 0
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#define PROC_ID_GROUP 1
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#define PROC_ID_SESSION 2
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#define PROC_ID_REAP 3
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void proc_id_set(int type, pid_t id);
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void proc_id_set_cond(int type, pid_t id);
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void proc_id_clear(int type, pid_t id);
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#endif /* _KERNEL */
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#endif /* !_SYS_PROC_H_ */
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