Commits
David Howells committed 9faaff59340
rxrpc: Provide a different lockdep key for call->user_mutex for kernel calls
Provide a different lockdep key for rxrpc_call::user_mutex when the call is
made on a kernel socket, such as by the AFS filesystem.
The problem is that lockdep registers a false positive between userspace
calling the sendmsg syscall on a user socket where call->user_mutex is held
whilst userspace memory is accessed whereas the AFS filesystem may perform
operations with mmap_sem held by the caller.
In such a case, the following warning is produced.
======================================================
WARNING: possible circular locking dependency detected
4.14.0-fscache+ #243 Tainted: G E
------------------------------------------------------
modpost/16701 is trying to acquire lock:
(&vnode->io_lock){+.+.}, at: [<ffffffffa000fc40>] afs_begin_vnode_operation+0x33/0x77 [kafs]
but task is already holding lock:
(&mm->mmap_sem){++++}, at: [<ffffffff8104376a>] __do_page_fault+0x1ef/0x486
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (&mm->mmap_sem){++++}:
__might_fault+0x61/0x89
_copy_from_iter_full+0x40/0x1fa
rxrpc_send_data+0x8dc/0xff3
rxrpc_do_sendmsg+0x62f/0x6a1
rxrpc_sendmsg+0x166/0x1b7
sock_sendmsg+0x2d/0x39
___sys_sendmsg+0x1ad/0x22b
__sys_sendmsg+0x41/0x62
do_syscall_64+0x89/0x1be
return_from_SYSCALL_64+0x0/0x75
-> #2 (&call->user_mutex){+.+.}:
__mutex_lock+0x86/0x7d2
rxrpc_new_client_call+0x378/0x80e
rxrpc_kernel_begin_call+0xf3/0x154
afs_make_call+0x195/0x454 [kafs]
afs_vl_get_capabilities+0x193/0x198 [kafs]
afs_vl_lookup_vldb+0x5f/0x151 [kafs]
afs_create_volume+0x2e/0x2f4 [kafs]
afs_mount+0x56a/0x8d7 [kafs]
mount_fs+0x6a/0x109
vfs_kern_mount+0x67/0x135
do_mount+0x90b/0xb57
SyS_mount+0x72/0x98
do_syscall_64+0x89/0x1be
return_from_SYSCALL_64+0x0/0x75
-> #1 (k-sk_lock-AF_RXRPC){+.+.}:
lock_sock_nested+0x74/0x8a
rxrpc_kernel_begin_call+0x8a/0x154
afs_make_call+0x195/0x454 [kafs]
afs_fs_get_capabilities+0x17a/0x17f [kafs]
afs_probe_fileserver+0xf7/0x2f0 [kafs]
afs_select_fileserver+0x83f/0x903 [kafs]
afs_fetch_status+0x89/0x11d [kafs]
afs_iget+0x16f/0x4f8 [kafs]
afs_mount+0x6c6/0x8d7 [kafs]
mount_fs+0x6a/0x109
vfs_kern_mount+0x67/0x135
do_mount+0x90b/0xb57
SyS_mount+0x72/0x98
do_syscall_64+0x89/0x1be
return_from_SYSCALL_64+0x0/0x75
-> #0 (&vnode->io_lock){+.+.}:
lock_acquire+0x174/0x19f
__mutex_lock+0x86/0x7d2
afs_begin_vnode_operation+0x33/0x77 [kafs]
afs_fetch_data+0x80/0x12a [kafs]
afs_readpages+0x314/0x405 [kafs]
__do_page_cache_readahead+0x203/0x2ba
filemap_fault+0x179/0x54d
__do_fault+0x17/0x60
__handle_mm_fault+0x6d7/0x95c
handle_mm_fault+0x24e/0x2a3
__do_page_fault+0x301/0x486
do_page_fault+0x236/0x259
page_fault+0x22/0x30
__clear_user+0x3d/0x60
padzero+0x1c/0x2b
load_elf_binary+0x785/0xdc7
search_binary_handler+0x81/0x1ff
do_execveat_common.isra.14+0x600/0x888
do_execve+0x1f/0x21
SyS_execve+0x28/0x2f
do_syscall_64+0x89/0x1be
return_from_SYSCALL_64+0x0/0x75
other info that might help us debug this:
Chain exists of:
&vnode->io_lock --> &call->user_mutex --> &mm->mmap_sem
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&mm->mmap_sem);
lock(&call->user_mutex);
lock(&mm->mmap_sem);
lock(&vnode->io_lock);
*** DEADLOCK ***
1 lock held by modpost/16701:
#0: (&mm->mmap_sem){++++}, at: [<ffffffff8104376a>] __do_page_fault+0x1ef/0x486
stack backtrace:
CPU: 0 PID: 16701 Comm: modpost Tainted: G E 4.14.0-fscache+ #243
Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
Call Trace:
dump_stack+0x67/0x8e
print_circular_bug+0x341/0x34f
check_prev_add+0x11f/0x5d4
? add_lock_to_list.isra.12+0x8b/0x8b
? add_lock_to_list.isra.12+0x8b/0x8b
? __lock_acquire+0xf77/0x10b4
__lock_acquire+0xf77/0x10b4
lock_acquire+0x174/0x19f
? afs_begin_vnode_operation+0x33/0x77 [kafs]
__mutex_lock+0x86/0x7d2
? afs_begin_vnode_operation+0x33/0x77 [kafs]
? afs_begin_vnode_operation+0x33/0x77 [kafs]
? afs_begin_vnode_operation+0x33/0x77 [kafs]
afs_begin_vnode_operation+0x33/0x77 [kafs]
afs_fetch_data+0x80/0x12a [kafs]
afs_readpages+0x314/0x405 [kafs]
__do_page_cache_readahead+0x203/0x2ba
? filemap_fault+0x179/0x54d
filemap_fault+0x179/0x54d
__do_fault+0x17/0x60
__handle_mm_fault+0x6d7/0x95c
handle_mm_fault+0x24e/0x2a3
__do_page_fault+0x301/0x486
do_page_fault+0x236/0x259
page_fault+0x22/0x30
RIP: 0010:__clear_user+0x3d/0x60
RSP: 0018:ffff880071e93da0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 000000000000011c RCX: 000000000000011c
RDX: 0000000000000000 RSI: 0000000000000008 RDI: 000000000060f720
RBP: 000000000060f720 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: ffff8800b5459b68 R12: ffff8800ce150e00
R13: 000000000060f720 R14: 00000000006127a8 R15: 0000000000000000
padzero+0x1c/0x2b
load_elf_binary+0x785/0xdc7
search_binary_handler+0x81/0x1ff
do_execveat_common.isra.14+0x600/0x888
do_execve+0x1f/0x21
SyS_execve+0x28/0x2f
do_syscall_64+0x89/0x1be
entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x7fdb6009ee07
RSP: 002b:00007fff566d9728 EFLAGS: 00000246 ORIG_RAX: 000000000000003b
RAX: ffffffffffffffda RBX: 000055ba57280900 RCX: 00007fdb6009ee07
RDX: 000055ba5727f270 RSI: 000055ba5727cac0 RDI: 000055ba57280900
RBP: 000055ba57280900 R08: 00007fff566d9700 R09: 0000000000000000
R10: 000055ba5727cac0 R11: 0000000000000246 R12: 0000000000000000
R13: 000055ba5727cac0 R14: 000055ba5727f270 R15: 0000000000000000
Signed-off-by: David Howells <dhowells@redhat.com>