[Xen-changelog] [xen stable-4.9] livepatch: Wrong usage of spinlock on debug console.

[patchbot@xxxxxxx]

commit 89b71d14621850c6c4b87a2cb3476efb069aeca9
Author:     Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
AuthorDate: Fri Jun 9 09:31:28 2017 -0400
Commit:     Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CommitDate: Mon Jun 12 09:06:03 2017 -0400

    livepatch: Wrong usage of spinlock on debug console.
    
    If we have a large amount of livepatches and want to print them
    on the console using 'xl debug-keys x' we eventually hit
    the preemption check:
    
      if ( i && !(i % 64) )
      {
        spin_unlock(&payload_lock);
        process_pending_softirqs();
        if ( spin_trylock(&payload_lock) )
                return
    
    <facepalm> The effect is that we have just effectively
    taken the lock and returned without unlocking!
    
    Reviewed-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
    Reviewed-and-tested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: Julien Grall <julien.grall@xxxxxxx>
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
    (cherry picked from commit 75dfe7c566c36e0af4714557a666827f49b69191)
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 xen/common/livepatch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c
index f14bcbc..df67a1a 100644
--- a/xen/common/livepatch.c
+++ b/xen/common/livepatch.c
@@ -1642,7 +1642,7 @@ static void livepatch_printall(unsigned char key)
             {
                 spin_unlock(&payload_lock);
                 process_pending_softirqs();
-                if ( spin_trylock(&payload_lock) )
+                if ( !spin_trylock(&payload_lock) )
                 {
                     printk("Couldn't reacquire lock. Try again.\n");
                     return;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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