diff --git a/kernel/core/sleeplock.c b/kernel/core/sleeplock.c
index 987dd34..f1eb5ed 100644
--- a/kernel/core/sleeplock.c
+++ b/kernel/core/sleeplock.c
@@ -45,11 +45,30 @@ releasesleep(struct sleeplock *lk)
   release(&lk->lk);
 }
 
+// Does *this process* hold lk?
+//
+// The pid comparison is not decoration. Without it this answers "is anyone
+// holding this", and every caller is an assertion of the form
+//
+//     if (!holdingsleep(&b->lock)) panic("brelse");
+//
+// whose entire purpose is to catch a process releasing a lock it never took.
+// Answering the weaker question disarms all seven of them: iunlock() on an
+// inode locked by another process, and brelse() on somebody else's buffer,
+// both sailed through and unlocked it underneath the real holder. Two
+// processes then believe they hold the same inode, and the corruption surfaces
+// somewhere else entirely -- which is exactly the shape of bug these panics
+// exist to prevent.
+//
+// myproc() is null on the boot path before the scheduler runs, and
+// acquiresleep() stores 0 for that case, so compare the same way rather than
+// dereferencing null here.
 int
 holdingsleep(struct sleeplock *lk)
 {
+  struct proc *p = myproc();
   acquire(&lk->lk);
-  int r = lk->locked;
+  int r = lk->locked && lk->pid == (p ? p->pid : 0);
   release(&lk->lk);
   return r;
 }