arm64: fix exec() deadlock by releasing ext2 lock before userspace jump #138
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The run_userspace_from_ext2() function acquires the ext2 root_fs() spinlock to load the init_shell ELF binary, but then jumps directly to userspace via ERET without returning. Since return_to_userspace() never returns, the MutexGuard is never dropped and the spinlock remains held forever. When userspace calls fork() then exec(), the child process tries to load the new program via load_elf_from_ext2(), which attempts to acquire the same spinlock - resulting in a deadlock. The fix adds an explicit drop(fs_guard) after reading the ELF data but before jumping to userspace. This releases the lock at the earliest safe point and allows subsequent exec() calls to succeed. This unblocks ~35 ARM64 tests that were hanging after exec(). Also includes: - Lock-free trace buffer (trace.rs) for debugging critical paths - Trace points in syscall_entry.rs for exec path debugging - ARM64 parity tracking document - Test infrastructure for ARM64 userspace tests Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
exec()run_userspace_from_ext2()held ext2 lock across non-returning ERET to userspacedrop(fs_guard)after ELF read, before userspace jumpRoot Cause Analysis
run_userspace_from_ext2()acquiresext2::root_fs()spinlockexec()deadlock trying to acquire the same lockChanges
kernel/src/main_aarch64.rs: Adddrop(fs_guard)after ELF data readkernel/src/arch_impl/aarch64/trace.rs: Lock-free trace buffer for debuggingkernel/src/arch_impl/aarch64/syscall_entry.rs: Trace points for exec patharm64-parity.md: ARM64 parity tracking documentTest plan
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