diff options
author | Johannes Berg <johannes.berg@intel.com> | 2019-05-24 21:54:14 +0200 |
---|---|---|
committer | Richard Weinberger <richard@nod.at> | 2019-07-02 23:27:11 +0200 |
commit | 80bf6ceaf9310b3f61934c69b382d4912deee049 (patch) | |
tree | 576b58e14d7c930173a3e4e80b247709831124e0 | |
parent | 8eacd6fca4044f470fc2eb0552ce6b8eab977e6c (diff) | |
download | linux-80bf6ceaf9310b3f61934c69b382d4912deee049.tar.gz linux-80bf6ceaf9310b3f61934c69b382d4912deee049.tar.bz2 linux-80bf6ceaf9310b3f61934c69b382d4912deee049.zip |
um: Silence lockdep complaint about mmap_sem
When we get into activate_mm(), lockdep complains that we're doing
something strange:
WARNING: possible circular locking dependency detected
5.1.0-10252-gb00152307319-dirty #121 Not tainted
------------------------------------------------------
inside.sh/366 is trying to acquire lock:
(____ptrval____) (&(&p->alloc_lock)->rlock){+.+.}, at: flush_old_exec+0x703/0x8d7
but task is already holding lock:
(____ptrval____) (&mm->mmap_sem){++++}, at: flush_old_exec+0x6c5/0x8d7
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&mm->mmap_sem){++++}:
[...]
__lock_acquire+0x12ab/0x139f
lock_acquire+0x155/0x18e
down_write+0x3f/0x98
flush_old_exec+0x748/0x8d7
load_elf_binary+0x2ca/0xddb
[...]
-> #0 (&(&p->alloc_lock)->rlock){+.+.}:
[...]
__lock_acquire+0x12ab/0x139f
lock_acquire+0x155/0x18e
_raw_spin_lock+0x30/0x83
flush_old_exec+0x703/0x8d7
load_elf_binary+0x2ca/0xddb
[...]
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&mm->mmap_sem);
lock(&(&p->alloc_lock)->rlock);
lock(&mm->mmap_sem);
lock(&(&p->alloc_lock)->rlock);
*** DEADLOCK ***
2 locks held by inside.sh/366:
#0: (____ptrval____) (&sig->cred_guard_mutex){+.+.}, at: __do_execve_file+0x12d/0x869
#1: (____ptrval____) (&mm->mmap_sem){++++}, at: flush_old_exec+0x6c5/0x8d7
stack backtrace:
CPU: 0 PID: 366 Comm: inside.sh Not tainted 5.1.0-10252-gb00152307319-dirty #121
Stack:
[...]
Call Trace:
[<600420de>] show_stack+0x13b/0x155
[<6048906b>] dump_stack+0x2a/0x2c
[<6009ae64>] print_circular_bug+0x332/0x343
[<6009c5c6>] check_prev_add+0x669/0xdad
[<600a06b4>] __lock_acquire+0x12ab/0x139f
[<6009f3d0>] lock_acquire+0x155/0x18e
[<604a07e0>] _raw_spin_lock+0x30/0x83
[<60151e6a>] flush_old_exec+0x703/0x8d7
[<601a8eb8>] load_elf_binary+0x2ca/0xddb
[...]
I think it's because in exec_mmap() we have
down_read(&old_mm->mmap_sem);
...
task_lock(tsk);
...
activate_mm(active_mm, mm);
(which does down_write(&mm->mmap_sem))
I'm not really sure why lockdep throws in the whole knowledge
about the task lock, but it seems that old_mm and mm shouldn't
ever be the same (and it doesn't deadlock) so tell lockdep that
they're different.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
-rw-r--r-- | arch/um/include/asm/mmu_context.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h index 9f4b4bb78120..00cefd33afdd 100644 --- a/arch/um/include/asm/mmu_context.h +++ b/arch/um/include/asm/mmu_context.h @@ -52,7 +52,7 @@ static inline void activate_mm(struct mm_struct *old, struct mm_struct *new) * when the new ->mm is used for the first time. */ __switch_mm(&new->context.id); - down_write(&new->mmap_sem); + down_write_nested(&new->mmap_sem, 1); uml_setup_stubs(new); up_write(&new->mmap_sem); } |