Module Name: src
Committed By: riastradh
Date: Tue Sep 7 16:56:25 UTC 2021
Modified Files:
src/sys/kern: kern_ksyms.c
Log Message:
Revert "ksyms(4): Simply block unload until last /dev/ksyms close."
This appears to break t_execsnoop -- presumably something goes wrong
with how libdtrace uses ksyms. To investigate.
To generate a diff of this commit:
cvs rdiff -u -r1.101 -r1.102 src/sys/kern/kern_ksyms.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_ksyms.c
diff -u src/sys/kern/kern_ksyms.c:1.101 src/sys/kern/kern_ksyms.c:1.102
--- src/sys/kern/kern_ksyms.c:1.101 Tue Sep 7 16:56:13 2021
+++ src/sys/kern/kern_ksyms.c Tue Sep 7 16:56:25 2021
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_ksyms.c,v 1.101 2021/09/07 16:56:13 riastradh Exp $ */
+/* $NetBSD: kern_ksyms.c,v 1.102 2021/09/07 16:56:25 riastradh Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -73,7 +73,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_ksyms.c,v 1.101 2021/09/07 16:56:13 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_ksyms.c,v 1.102 2021/09/07 16:56:25 riastradh Exp $");
#if defined(_KERNEL) && defined(_KERNEL_OPT)
#include "opt_copy_symtab.h"
@@ -117,7 +117,6 @@ static struct ksyms_symtab *ksyms_last_s
static bool ksyms_initted;
static bool ksyms_loaded;
static kmutex_t ksyms_lock __cacheline_aligned;
-static kcondvar_t ksyms_cv;
static struct ksyms_symtab kernel_symtab;
static void ksyms_hdr_init(const void *);
@@ -246,7 +245,6 @@ ksyms_init(void)
if (!ksyms_initted) {
mutex_init(&ksyms_lock, MUTEX_DEFAULT, IPL_NONE);
- cv_init(&ksyms_cv, "ksyms");
ksyms_initted = true;
}
}
@@ -330,6 +328,7 @@ addsymtab(const char *name, void *symsta
tab->sd_minsym = UINTPTR_MAX;
tab->sd_maxsym = 0;
tab->sd_usroffset = 0;
+ tab->sd_gone = false;
tab->sd_ctfstart = ctfstart;
tab->sd_ctfsize = ctfsize;
tab->sd_nmap = nmap;
@@ -447,9 +446,9 @@ addsymtab(const char *name, void *symsta
KASSERT(cold || mutex_owned(&ksyms_lock));
/*
- * Publish the symtab. Do this at splhigh to ensure ddb never
- * witnesses an inconsistent state of the queue, unless memory
- * is so corrupt that we crash in TAILQ_INSERT_TAIL.
+ * Ensure ddb never witnesses an inconsistent state of the
+ * queue, unless memory is so corrupt that we crash in
+ * TAILQ_INSERT_TAIL.
*/
s = splhigh();
TAILQ_INSERT_TAIL(&ksyms_symtabs, tab, sd_queue);
@@ -602,6 +601,8 @@ ksyms_getval_unlocked(const char *mod, c
#endif
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (__predict_false(st->sd_gone))
+ continue;
if (mod != NULL && strcmp(st->sd_name, mod))
continue;
if ((es = findsym(sym, st, type)) != NULL) {
@@ -635,6 +636,8 @@ ksyms_get_mod(const char *mod)
mutex_enter(&ksyms_lock);
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (__predict_false(st->sd_gone))
+ continue;
if (mod != NULL && strcmp(st->sd_name, mod))
continue;
break;
@@ -668,6 +671,8 @@ ksyms_mod_foreach(const char *mod, ksyms
/* find the module */
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (__predict_false(st->sd_gone))
+ continue;
if (mod != NULL && strcmp(st->sd_name, mod))
continue;
@@ -711,6 +716,8 @@ ksyms_getname(const char **mod, const ch
return ENOENT;
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (st->sd_gone)
+ continue;
if (v < st->sd_minsym || v > st->sd_maxsym)
continue;
sz = st->sd_symsize/sizeof(Elf_Sym);
@@ -773,44 +780,37 @@ void
ksyms_modunload(const char *name)
{
struct ksyms_symtab *st;
+ bool do_free = false;
int s;
mutex_enter(&ksyms_lock);
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (st->sd_gone)
+ continue;
if (strcmp(name, st->sd_name) != 0)
continue;
+ st->sd_gone = true;
+ ksyms_sizes_calc();
+ if (ksyms_opencnt == 0) {
+ /*
+ * Ensure ddb never witnesses an inconsistent
+ * state of the queue, unless memory is so
+ * corrupt that we crash in TAILQ_REMOVE.
+ */
+ s = splhigh();
+ TAILQ_REMOVE(&ksyms_symtabs, st, sd_queue);
+ splx(s);
+ do_free = true;
+ }
break;
}
- KASSERT(st != NULL);
-
- /*
- * Wait for last /dev/ksyms close -- readers may be in the
- * middle of viewing a snapshot including this module. (We
- * could skip this if it's past ksyms_last_snapshot, but it's
- * not clear that's worth the effort.)
- */
- while (ksyms_opencnt)
- cv_wait(&ksyms_cv, &ksyms_lock);
-
- /*
- * Remove the symtab. Do this at splhigh to ensure ddb never
- * witnesses an inconsistent state of the queue, unless memory
- * is so corrupt that we crash in TAILQ_REMOVE.
- */
- s = splhigh();
- TAILQ_REMOVE(&ksyms_symtabs, st, sd_queue);
- splx(s);
-
- /* Recompute the ksyms sizes now that we've removed st. */
- ksyms_sizes_calc();
mutex_exit(&ksyms_lock);
+ KASSERT(st != NULL);
- /*
- * No more references are possible. Free the name map and the
- * symtab itself, which we had allocated in ksyms_modload.
- */
- kmem_free(st->sd_nmap, st->sd_nmapsize * sizeof(uint32_t));
- kmem_free(st, sizeof(*st));
+ if (do_free) {
+ kmem_free(st->sd_nmap, st->sd_nmapsize * sizeof(uint32_t));
+ kmem_free(st, sizeof(*st));
+ }
}
#ifdef DDB
@@ -830,6 +830,8 @@ ksyms_sift(char *mod, char *sym, int mod
return ENOENT;
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (st->sd_gone)
+ continue;
if (mod && strcmp(mod, st->sd_name))
continue;
sb = st->sd_strstart - st->sd_usroffset;
@@ -891,6 +893,8 @@ ksyms_sizes_calc(void)
ksyms_symsz = ksyms_strsz = 0;
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (__predict_false(st->sd_gone))
+ continue;
delta = ksyms_strsz - st->sd_usroffset;
if (delta != 0) {
for (i = 0; i < st->sd_symsize/sizeof(Elf_Sym); i++)
@@ -1023,14 +1027,37 @@ out: mutex_exit(&ksyms_lock);
static int
ksymsclose(dev_t dev, int oflags, int devtype, struct lwp *l)
{
+ struct ksyms_symtab *st, *next;
+ TAILQ_HEAD(, ksyms_symtab) to_free = TAILQ_HEAD_INITIALIZER(to_free);
+ int s;
+ /* Discard references to symbol tables. */
mutex_enter(&ksyms_lock);
if (--ksyms_opencnt)
goto out;
ksyms_last_snapshot = NULL;
- cv_broadcast(&ksyms_cv);
+ TAILQ_FOREACH_SAFE(st, &ksyms_symtabs, sd_queue, next) {
+ if (st->sd_gone) {
+ /*
+ * Ensure ddb never witnesses an inconsistent
+ * state of the queue, unless memory is so
+ * corrupt that we crash in TAILQ_REMOVE.
+ */
+ s = splhigh();
+ TAILQ_REMOVE(&ksyms_symtabs, st, sd_queue);
+ splx(s);
+ TAILQ_INSERT_TAIL(&to_free, st, sd_queue);
+ }
+ }
+ if (!TAILQ_EMPTY(&to_free))
+ ksyms_sizes_calc();
out: mutex_exit(&ksyms_lock);
+ TAILQ_FOREACH_SAFE(st, &to_free, sd_queue, next) {
+ kmem_free(st->sd_nmap, st->sd_nmapsize * sizeof(uint32_t));
+ kmem_free(st, sizeof(*st));
+ }
+
return 0;
}
@@ -1042,7 +1069,8 @@ ksymsread(dev_t dev, struct uio *uio, in
int error;
/*
- * First: Copy out the ELF header.
+ * First: Copy out the ELF header. XXX Lose if ksymsopen()
+ * occurs during read of the header.
*/
off = uio->uio_offset;
if (off < sizeof(struct ksyms_hdr)) {
@@ -1053,17 +1081,12 @@ ksymsread(dev_t dev, struct uio *uio, in
}
/*
- * Copy out the symbol table. The list of symtabs is
- * guaranteed to be nonempty because we always have an entry
- * for the main kernel. We stop at ksyms_last_snapshot, not at
- * the end of the tailq or NULL, because entries beyond
- * ksyms_last_snapshot are not included in this snapshot (and
- * may not be fully initialized memory as we witness it).
+ * Copy out the symbol table.
*/
filepos = sizeof(struct ksyms_hdr);
- for (st = TAILQ_FIRST(&ksyms_symtabs);
- ;
- st = TAILQ_NEXT(st, sd_queue)) {
+ TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (__predict_false(st->sd_gone))
+ continue;
if (uio->uio_resid == 0)
return 0;
if (uio->uio_offset <= st->sd_symsize + filepos) {
@@ -1102,8 +1125,6 @@ ksymsread(dev_t dev, struct uio *uio, in
/*
* Copy out the CTF table.
- *
- * XXX Why does this only copy out the first symtab's CTF?
*/
st = TAILQ_FIRST(&ksyms_symtabs);
if (st->sd_ctfstart != NULL) {
@@ -1175,6 +1196,8 @@ ksymsioctl(dev_t dev, u_long cmd, void *
*/
mutex_enter(&ksyms_lock);
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (st->sd_gone)
+ continue;
if ((sym = findsym(str, st, KSYMS_ANY)) == NULL)
continue;
#ifdef notdef
@@ -1215,6 +1238,8 @@ ksymsioctl(dev_t dev, u_long cmd, void *
*/
mutex_enter(&ksyms_lock);
TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
+ if (st->sd_gone)
+ continue;
if ((sym = findsym(str, st, KSYMS_ANY)) == NULL)
continue;
#ifdef notdef
