CHROMIUM: ramoops: Copy the entire buffer to deal with bit rot

If unclean shutdown is done by yanking power rails, the RAM may be in a
state where it is not getting refreshed for a short period of time. This
can cause bit rotting in RAM and throw off the wraparound and buffer
size calculation logic. To get around this, copy the entire console
buffer. Note that this, of course, won't do anything to fix the bit
rotting but the intent here is that some logs are better than none.

Also squeezed in a minor cleanup of renaming headp to tailp since it
really tracks the tail, not head.

BUG=chrome-os-partner:13249
TEST=on a snow system do a warm reboot by either issuing the
"warm_reboot" command from servo ec console or by pressing
alt-volume_up-r keys together. The system should reboot. Upon bootup,
check contents of "/dev/pstore/console-ramoops" and ensure they are from
dmesg of the previous boot.

Change-Id: I999e95bf854fff26265404a680255f25cc2f7fe6
Signed-off-by: Sameer Nanda <snanda@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/31909
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>

diff --git a/drivers/char/ramoops.c b/drivers/char/ramoops.c
index fa353e3..6a59d9b 100644 (file)
--- a/drivers/char/ramoops.c
+++ b/drivers/char/ramoops.c
@@ -55,7 +55,7 @@ struct ramoops_context {
 #ifdef CONFIG_PSTORE_CONSOLE
        char *old_con_buf;
        char *con_buf;
-       size_t *con_headp;
+       size_t *con_tailp;
        size_t con_size;
 #endif
        phys_addr_t phys_addr;
@@ -118,11 +118,15 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
        time->tv_nsec = 0;
 
        rambuf = cxt->virt_addr + (*id * cxt->record_size);
+       size = strnlen(rambuf, cxt->record_size);
+
 #ifdef CONFIG_PSTORE_CONSOLE
-       if (*type == PSTORE_TYPE_CONSOLE)
+       if (*type == PSTORE_TYPE_CONSOLE) {
                rambuf = cxt->old_con_buf;
+               /* Grab entire buffer to deal with RAM bit rot. */
+               size = cxt->record_size;
+       }
 #endif
-       size = strnlen(rambuf, cxt->record_size);
        *buf = kmalloc(size, GFP_KERNEL);
        if (*buf == NULL)
                return -ENOMEM;
@@ -145,25 +149,25 @@ static int ramoops_pstore_write(enum pstore_type_id type,
 
 #ifdef CONFIG_PSTORE_CONSOLE
        if (type == PSTORE_TYPE_CONSOLE) {
-               size_t head = *cxt->con_headp;
+               size_t tail = *cxt->con_tailp;
                size_t bytes;
 
                if (size >= cxt->con_size) {
                        buf = cxt->pstore.buf + size - cxt->con_size;
                        memcpy(cxt->con_buf, buf, cxt->con_size);
-                       *cxt->con_headp = 0;
+                       *cxt->con_tailp = 0;
                        return 0;
                }
-               bytes = min(size, cxt->con_size - head);
-               memcpy(cxt->con_buf + head, cxt->pstore.buf, bytes);
+               bytes = min(size, cxt->con_size - tail);
+               memcpy(cxt->con_buf + tail, cxt->pstore.buf, bytes);
                size -= bytes;
                if (size)
                        memcpy(cxt->con_buf, cxt->pstore.buf + bytes, size);
                else
-                       size = head + bytes;
+                       size = tail + bytes;
                if (size == cxt->con_size)
                        size = 0;
-               *cxt->con_headp = size;
+               *cxt->con_tailp = size;
                return 0;
        }
 #endif
@@ -335,19 +339,20 @@ static int __init ramoops_probe(struct platform_device *pdev)
        }
        cxt->con_buf = cxt->virt_addr + (cxt->max_count - 1) * cxt->record_size;
        cxt->con_size = cxt->record_size - sizeof(size_t);
-       cxt->con_headp = (size_t *)(cxt->con_buf + cxt->con_size);
+       cxt->con_tailp = (size_t *)(cxt->con_buf + cxt->con_size);
        cxt->old_con_buf[0] = '\0';
-       if (*cxt->con_headp < cxt->con_size) {
-               size_t head = *cxt->con_headp;
-               size_t size = cxt->con_size - head;
+       if (*cxt->con_tailp < cxt->con_size) {
+               size_t tail = *cxt->con_tailp;
+               size_t size = cxt->con_size - tail;
 
-               if (cxt->con_buf[head] != '\0')
-                       memcpy(cxt->old_con_buf, cxt->con_buf + head, size);
+               if (cxt->con_buf[tail] != '\0')
+                       memcpy(cxt->old_con_buf, cxt->con_buf + tail, size);
                else
                        size = 0;
-               if (head)
-                       memcpy(cxt->old_con_buf + size, cxt->con_buf, head);
-               cxt->old_con_buf[size + head] = '\0';
+
+               if (tail)
+                       memcpy(cxt->old_con_buf + size, cxt->con_buf, tail);
+               cxt->old_con_buf[size + tail] = '\0';
        }
        memset(cxt->con_buf, '\0', cxt->record_size);
 #endif