pstore: Convert buf_lock to semaphore

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>

diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 22e9d28..e7d4ce6 100644 (file)
--- 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 */

diff --git a/drivers/acpi/apei/erst.c b/drivers/acpi/apei/erst.c
index a5e1d96..9953e50 100644 (file)
--- 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 -

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index cfe87b4..0f7d979 100644 (file)
--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -259,8 +259,7 @@ static int efi_pstore_write(struct pstore_record *record)
                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(void)
                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);

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 2387cb7..2d1066e 100644 (file)
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -161,26 +161,27 @@ static const char *get_reason_str(enum kmsg_dump_reason reason)
        }
 }
 
-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)
@@ -400,23 +401,23 @@ static void pstore_dump(struct kmsg_dumper *dumper,
        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;
@@ -433,7 +434,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
                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 {
@@ -451,7 +452,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
                                          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);
@@ -474,8 +475,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
                total += record.size;
                part++;
        }
-       if (is_locked)
-               spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+
+       up(&psinfo->buf_lock);
 }
 
 static struct kmsg_dumper pstore_dumper = {
@@ -594,6 +595,7 @@ int pstore_register(struct pstore_info *psi)
                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)) {

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 202eaa8..e6d9560 100644 (file)
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -815,7 +815,6 @@ static int ramoops_probe(struct platform_device *pdev)
                err = -ENOMEM;
                goto fail_clear;
        }
-       spin_lock_init(&cxt->pstore.buf_lock);
 
        cxt->pstore.flags = PSTORE_FLAGS_DMESG;
        if (cxt->console_size)

diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index a9ec285..b146181 100644 (file)
--- 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>
 
@@ -99,7 +99,7 @@ struct pstore_record {
  * @owner:     module which is responsible 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
@@ -184,7 +184,7 @@ struct pstore_info {
        struct module   *owner;
        char            *name;
 
-       spinlock_t      buf_lock;
+       struct semaphore buf_lock;
        char            *buf;
        size_t          bufsize;
 
@@ -210,7 +210,6 @@ 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;