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Subject[PATCH 4.19 24/51] pstore: Convert buf_lock to semaphore
Date
From: Kees Cook <keescook@chromium.org>

commit ea84b580b95521644429cc6748b6c2bf27c8b0f3 upstream.

Instead of running with interrupts disabled, use a semaphore. This should
make it easier for backends that may need to sleep (e.g. EFI) when
performing a write:

|BUG: sleeping function called from invalid context at kernel/sched/completion.c:99
|in_atomic(): 1, irqs_disabled(): 1, pid: 2236, name: sig-xstate-bum
|Preemption disabled at:
|[<ffffffff99d60512>] pstore_dump+0x72/0x330
|CPU: 26 PID: 2236 Comm: sig-xstate-bum Tainted: G D 4.20.0-rc3 #45
|Call Trace:
| dump_stack+0x4f/0x6a
| ___might_sleep.cold.91+0xd3/0xe4
| __might_sleep+0x50/0x90
| wait_for_completion+0x32/0x130
| virt_efi_query_variable_info+0x14e/0x160
| efi_query_variable_store+0x51/0x1a0
| efivar_entry_set_safe+0xa3/0x1b0
| efi_pstore_write+0x109/0x140
| pstore_dump+0x11c/0x330
| kmsg_dump+0xa4/0xd0
| oops_exit+0x22/0x30
...

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Fixes: 21b3ddd39fee ("efi: Don't use spinlocks for efi vars")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/kernel/nvram_64.c | 2 -
drivers/acpi/apei/erst.c | 1
drivers/firmware/efi/efi-pstore.c | 4 ---
fs/pstore/platform.c | 44 +++++++++++++++++++-------------------
fs/pstore/ram.c | 1
include/linux/pstore.h | 7 ++----
6 files changed, 27 insertions(+), 32 deletions(-)

--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -563,8 +563,6 @@ static int nvram_pstore_init(void)
nvram_pstore_info.buf = oops_data;
nvram_pstore_info.bufsize = oops_data_sz;

- spin_lock_init(&nvram_pstore_info.buf_lock);
-
rc = pstore_register(&nvram_pstore_info);
if (rc && (rc != -EPERM))
/* Print error only when pstore.backend == nvram */
--- a/drivers/acpi/apei/erst.c
+++ b/drivers/acpi/apei/erst.c
@@ -1176,7 +1176,6 @@ static int __init erst_init(void)
"Error Record Serialization Table (ERST) support is initialized.\n");

buf = kmalloc(erst_erange.size, GFP_KERNEL);
- spin_lock_init(&erst_info.buf_lock);
if (buf) {
erst_info.buf = buf + sizeof(struct cper_pstore_record);
erst_info.bufsize = erst_erange.size -
--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -259,8 +259,7 @@ static int efi_pstore_write(struct pstor
efi_name[i] = name[i];

ret = efivar_entry_set_safe(efi_name, vendor, PSTORE_EFI_ATTRIBUTES,
- !pstore_cannot_block_path(record->reason),
- record->size, record->psi->buf);
+ preemptible(), record->size, record->psi->buf);

if (record->reason == KMSG_DUMP_OOPS)
efivar_run_worker();
@@ -369,7 +368,6 @@ static __init int efivars_pstore_init(vo
return -ENOMEM;

efi_pstore_info.bufsize = 1024;
- spin_lock_init(&efi_pstore_info.buf_lock);

if (pstore_register(&efi_pstore_info)) {
kfree(efi_pstore_info.buf);
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -124,26 +124,27 @@ static const char *get_reason_str(enum k
}
}

-bool pstore_cannot_block_path(enum kmsg_dump_reason reason)
+/*
+ * Should pstore_dump() wait for a concurrent pstore_dump()? If
+ * not, the current pstore_dump() will report a failure to dump
+ * and return.
+ */
+static bool pstore_cannot_wait(enum kmsg_dump_reason reason)
{
- /*
- * In case of NMI path, pstore shouldn't be blocked
- * regardless of reason.
- */
+ /* In NMI path, pstore shouldn't block regardless of reason. */
if (in_nmi())
return true;

switch (reason) {
/* In panic case, other cpus are stopped by smp_send_stop(). */
case KMSG_DUMP_PANIC:
- /* Emergency restart shouldn't be blocked by spin lock. */
+ /* Emergency restart shouldn't be blocked. */
case KMSG_DUMP_EMERG:
return true;
default:
return false;
}
}
-EXPORT_SYMBOL_GPL(pstore_cannot_block_path);

#if IS_ENABLED(CONFIG_PSTORE_DEFLATE_COMPRESS)
static int zbufsize_deflate(size_t size)
@@ -378,23 +379,23 @@ static void pstore_dump(struct kmsg_dump
unsigned long total = 0;
const char *why;
unsigned int part = 1;
- unsigned long flags = 0;
- int is_locked;
int ret;

why = get_reason_str(reason);

- if (pstore_cannot_block_path(reason)) {
- is_locked = spin_trylock_irqsave(&psinfo->buf_lock, flags);
- if (!is_locked) {
- pr_err("pstore dump routine blocked in %s path, may corrupt error record\n"
- , in_nmi() ? "NMI" : why);
+ if (down_trylock(&psinfo->buf_lock)) {
+ /* Failed to acquire lock: give up if we cannot wait. */
+ if (pstore_cannot_wait(reason)) {
+ pr_err("dump skipped in %s path: may corrupt error record\n",
+ in_nmi() ? "NMI" : why);
+ return;
+ }
+ if (down_interruptible(&psinfo->buf_lock)) {
+ pr_err("could not grab semaphore?!\n");
return;
}
- } else {
- spin_lock_irqsave(&psinfo->buf_lock, flags);
- is_locked = 1;
}
+
oopscount++;
while (total < kmsg_bytes) {
char *dst;
@@ -411,7 +412,7 @@ static void pstore_dump(struct kmsg_dump
record.part = part;
record.buf = psinfo->buf;

- if (big_oops_buf && is_locked) {
+ if (big_oops_buf) {
dst = big_oops_buf;
dst_size = big_oops_buf_sz;
} else {
@@ -429,7 +430,7 @@ static void pstore_dump(struct kmsg_dump
dst_size, &dump_size))
break;

- if (big_oops_buf && is_locked) {
+ if (big_oops_buf) {
zipped_len = pstore_compress(dst, psinfo->buf,
header_size + dump_size,
psinfo->bufsize);
@@ -452,8 +453,8 @@ static void pstore_dump(struct kmsg_dump
total += record.size;
part++;
}
- if (is_locked)
- spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+
+ up(&psinfo->buf_lock);
}

static struct kmsg_dumper pstore_dumper = {
@@ -572,6 +573,7 @@ int pstore_register(struct pstore_info *
psi->write_user = pstore_write_user_compat;
psinfo = psi;
mutex_init(&psinfo->read_mutex);
+ sema_init(&psinfo->buf_lock, 1);
spin_unlock(&pstore_lock);

if (owner && !try_module_get(owner)) {
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -814,7 +814,6 @@ static int ramoops_probe(struct platform
err = -ENOMEM;
goto fail_clear;
}
- spin_lock_init(&cxt->pstore.buf_lock);

cxt->pstore.flags = PSTORE_FLAGS_DMESG;
if (cxt->console_size)
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -26,7 +26,7 @@
#include <linux/errno.h>
#include <linux/kmsg_dump.h>
#include <linux/mutex.h>
-#include <linux/spinlock.h>
+#include <linux/semaphore.h>
#include <linux/time.h>
#include <linux/types.h>

@@ -88,7 +88,7 @@ struct pstore_record {
* @owner: module which is repsonsible for this backend driver
* @name: name of the backend driver
*
- * @buf_lock: spinlock to serialize access to @buf
+ * @buf_lock: semaphore to serialize access to @buf
* @buf: preallocated crash dump buffer
* @bufsize: size of @buf available for crash dump bytes (must match
* smallest number of bytes available for writing to a
@@ -173,7 +173,7 @@ struct pstore_info {
struct module *owner;
char *name;

- spinlock_t buf_lock;
+ struct semaphore buf_lock;
char *buf;
size_t bufsize;

@@ -199,7 +199,6 @@ struct pstore_info {

extern int pstore_register(struct pstore_info *);
extern void pstore_unregister(struct pstore_info *);
-extern bool pstore_cannot_block_path(enum kmsg_dump_reason reason);

struct pstore_ftrace_record {
unsigned long ip;

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