Patch "pstore/core: drop cmpxchg based updates" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    pstore/core: drop cmpxchg based updates

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pstore-core-drop-cmpxchg-based-updates.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From d5a9bf0b38d2ac85c9a693c7fb851f74fd2a2494 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 8 Sep 2016 13:48:06 +0200
Subject: pstore/core: drop cmpxchg based updates
MIME-Version: 1.0
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

commit d5a9bf0b38d2ac85c9a693c7fb851f74fd2a2494 upstream.

I have here a FPGA behind PCIe which exports SRAM which I use for
pstore. Now it seems that the FPGA no longer supports cmpxchg based
updates and writes back 0xff…ff and returns the same.  This leads to
crash during crash rendering pstore useless.
Since I doubt that there is much benefit from using cmpxchg() here, I am
dropping this atomic access and use the spinlock based version.

Cc: Anton Vorontsov <anton@enomsg.org>
Cc: Colin Cross <ccross@android.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Rabin Vincent <rabinv@axis.com>
Tested-by: Rabin Vincent <rabinv@axis.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
[kees: remove "_locked" suffix since it's the only option now]
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/pstore/ram_core.c |   43 ++-----------------------------------------
 1 file changed, 2 insertions(+), 41 deletions(-)

--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -47,43 +47,10 @@ static inline size_t buffer_start(struct
 	return atomic_read(&prz->buffer->start);
 }
 
-/* increase and wrap the start pointer, returning the old value */
-static size_t buffer_start_add_atomic(struct persistent_ram_zone *prz, size_t a)
-{
-	int old;
-	int new;
-
-	do {
-		old = atomic_read(&prz->buffer->start);
-		new = old + a;
-		while (unlikely(new >= prz->buffer_size))
-			new -= prz->buffer_size;
-	} while (atomic_cmpxchg(&prz->buffer->start, old, new) != old);
-
-	return old;
-}
-
-/* increase the size counter until it hits the max size */
-static void buffer_size_add_atomic(struct persistent_ram_zone *prz, size_t a)
-{
-	size_t old;
-	size_t new;
-
-	if (atomic_read(&prz->buffer->size) == prz->buffer_size)
-		return;
-
-	do {
-		old = atomic_read(&prz->buffer->size);
-		new = old + a;
-		if (new > prz->buffer_size)
-			new = prz->buffer_size;
-	} while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);
-}
-
 static DEFINE_RAW_SPINLOCK(buffer_lock);
 
 /* increase and wrap the start pointer, returning the old value */
-static size_t buffer_start_add_locked(struct persistent_ram_zone *prz, size_t a)
+static size_t buffer_start_add(struct persistent_ram_zone *prz, size_t a)
 {
 	int old;
 	int new;
@@ -103,7 +70,7 @@ static size_t buffer_start_add_locked(st
 }
 
 /* increase the size counter until it hits the max size */
-static void buffer_size_add_locked(struct persistent_ram_zone *prz, size_t a)
+static void buffer_size_add(struct persistent_ram_zone *prz, size_t a)
 {
 	size_t old;
 	size_t new;
@@ -124,9 +91,6 @@ exit:
 	raw_spin_unlock_irqrestore(&buffer_lock, flags);
 }
 
-static size_t (*buffer_start_add)(struct persistent_ram_zone *, size_t) = buffer_start_add_atomic;
-static void (*buffer_size_add)(struct persistent_ram_zone *, size_t) = buffer_size_add_atomic;
-
 static void notrace persistent_ram_encode_rs8(struct persistent_ram_zone *prz,
 	uint8_t *data, size_t len, uint8_t *ecc)
 {
@@ -426,9 +390,6 @@ static void *persistent_ram_iomap(phys_a
 		return NULL;
 	}
 
-	buffer_start_add = buffer_start_add_locked;
-	buffer_size_add = buffer_size_add_locked;
-
 	if (memtype)
 		va = ioremap(start, size);
 	else


Patches currently in stable-queue which might be from bigeasy@linutronix.de are

queue-4.4/pstore-core-drop-cmpxchg-based-updates.patch
queue-4.4/pstore-ramoops-fixup-driver-removal.patch