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authorJohannes Berg <johannes.berg@intel.com>2019-05-24 21:54:14 +0200
committerRichard Weinberger <richard@nod.at>2019-07-02 23:27:11 +0200
commit80bf6ceaf9310b3f61934c69b382d4912deee049 (patch)
tree576b58e14d7c930173a3e4e80b247709831124e0 /arch/um
parent8eacd6fca4044f470fc2eb0552ce6b8eab977e6c (diff)
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>
Diffstat (limited to 'arch/um')
-rw-r--r--arch/um/include/asm/mmu_context.h2
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);
}