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

powerpc/opal: Fix EBUSY bug in acquiring tokens

to the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: powerpc-opal-fix-ebusy-bug-in-acquiring-tokens.patch and it can be found in the queue-3.18 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 foo@baz Mon Dec 18 15:03:25 CET 2017

From: "William A. Kennington III" wak@google.com Date: Fri, 22 Sep 2017 16:58:00 -0700 Subject: powerpc/opal: Fix EBUSY bug in acquiring tokens

From: "William A. Kennington III" wak@google.com

[ Upstream commit 71e24d7731a2903b1ae2bba2b2971c654d9c2aa6 ]

The current code checks the completion map to look for the first token that is complete. In some cases, a completion can come in but the token can still be on lease to the caller processing the completion. If this completed but unreleased token is the first token found in the bitmap by another tasks trying to acquire a token, then the __test_and_set_bit call will fail since the token will still be on lease. The acquisition will then fail with an EBUSY.

This patch reorganizes the acquisition code to look at the opal_async_token_map for an unleased token. If the token has no lease it must have no outstanding completions so we should never see an EBUSY, unless we have leased out too many tokens. Since opal_async_get_token_inrerruptible is protected by a semaphore, we will practically never see EBUSY anymore.

Fixes: 8d7248232208 ("powerpc/powernv: Infrastructure to support OPAL async completion") Signed-off-by: William A. Kennington III wak@google.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/platforms/powernv/opal-async.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/powerpc/platforms/powernv/opal-async.c +++ b/arch/powerpc/platforms/powernv/opal-async.c @@ -39,18 +39,18 @@ int __opal_async_get_token(void) int token;

spin_lock_irqsave(&opal_async_comp_lock, flags); - token = find_first_bit(opal_async_complete_map, opal_max_async_tokens); + token = find_first_zero_bit(opal_async_token_map, opal_max_async_tokens); if (token >= opal_max_async_tokens) { token = -EBUSY; goto out; }

- if (__test_and_set_bit(token, opal_async_token_map)) { + if (!__test_and_clear_bit(token, opal_async_complete_map)) { token = -EBUSY; goto out; }

- __clear_bit(token, opal_async_complete_map); + __set_bit(token, opal_async_token_map);

out: spin_unlock_irqrestore(&opal_async_comp_lock, flags);

Patches currently in stable-queue which might be from wak@google.com are

queue-3.18/powerpc-opal-fix-ebusy-bug-in-acquiring-tokens.patch