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SubjectRe: "tvec_bases too large for per-cpu data" commit broke early_serial_setup()
Eugene Surovegin <ebs@ebshome.net> wrote:
>
> Commit
> a4a6198b80cf82eb8160603c98da218d1bd5e104
> "[PATCH] tvec_bases too large for per-cpu data"
>
> broke early_serial_setup() and maybe other code which uses
> init_timer() before init_timers_cpu() is called.
>
> This commit introduced run-time initialization dependence which never
> existed before, namely, tvec_bases was always valid before this
> change, but now it's a pointer which should be initialized prior to
> use of any timer function.
>
> If init_timer() is called before such initialization (in my case this
> happens when PPC440GX board support code calls early_serial_setup to
> register UARTs, serial8250_isa_init_ports() calls init_timer()),
> "base" field in the timer_list struct is set to NULL.
>
> When later mod_timer() is called for such timer it hangs in
> lock_timer_base().
>
> Rolling back this commit fixes the problem, although, this is
> obviously not a proper fix.
>

Thanks. Early boot is ugly.

Does this fix it?



From: Andrew Morton <akpm@osdl.org>

We need the boot CPU's tvec_bases[] entry to be initialised super-early in
boot, for early_serial_setup(). That runs within setup_arch(), before even
per-cpu areas are initialised.

The patch changes tvec_bases to use compile-time initialisation, and adds a
separate array `tvec_base_done' to keep track of which CPU has had its
tvec_bases[] entry initialised (because we can no longer use the zeroness of
that tvec_bases[] entry to determine whether it has been initialised).

Thanks to Eugene Surovegin <ebs@ebshome.net> for diagnosing this.

Cc: Eugene Surovegin <ebs@ebshome.net>
Cc: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
kernel/timer.c | 29 +++++++++++++++++++----------
1 files changed, 19 insertions(+), 10 deletions(-)
diff -puN kernel/timer.c~timer-initialisation-fix kernel/timer.c
--- devel/kernel/timer.c~timer-initialisation-fix 2006-04-01 14:04:00.000000000 -0800
+++ devel-akpm/kernel/timer.c 2006-04-01 14:04:00.000000000 -0800
@@ -81,9 +81,11 @@ struct tvec_t_base_s {
} ____cacheline_aligned_in_smp;

typedef struct tvec_t_base_s tvec_base_t;
-static DEFINE_PER_CPU(tvec_base_t *, tvec_bases);
+
tvec_base_t boot_tvec_bases;
EXPORT_SYMBOL(boot_tvec_bases);
+static DEFINE_PER_CPU(tvec_base_t *, tvec_bases) = { &boot_tvec_bases };
+static char tvec_base_done[NR_CPUS];

static inline void set_running_timer(tvec_base_t *base,
struct timer_list *timer)
@@ -1225,27 +1227,34 @@ static int __devinit init_timers_cpu(int
int j;
tvec_base_t *base;

- base = per_cpu(tvec_bases, cpu);
- if (!base) {
+ if (!tvec_base_done[cpu]) {
static char boot_done;

- /*
- * Cannot do allocation in init_timers as that runs before the
- * allocator initializes (and would waste memory if there are
- * more possible CPUs than will ever be installed/brought up).
- */
if (boot_done) {
+ /*
+ * The APs use this path later in boot
+ */
base = kmalloc_node(sizeof(*base), GFP_KERNEL,
cpu_to_node(cpu));
if (!base)
return -ENOMEM;
memset(base, 0, sizeof(*base));
+ per_cpu(tvec_bases, cpu) = base;
} else {
- base = &boot_tvec_bases;
+ /*
+ * This is for the boot CPU - we use compile-time
+ * static initialisation because per-cpu memory isn't
+ * ready yet and because the memory allocators are not
+ * initialised either.
+ */
boot_done = 1;
+ base = &boot_tvec_bases;
}
- per_cpu(tvec_bases, cpu) = base;
+ tvec_base_done[cpu] = 1;
+ } else {
+ base = per_cpu(tvec_bases, cpu);
}
+
spin_lock_init(&base->lock);
for (j = 0; j < TVN_SIZE; j++) {
INIT_LIST_HEAD(base->tv5.vec + j);
_
-
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