io_uring: fix potential ABBA deadlock in ->show_fdinfo()
syzbot reports a potential lock deadlock between the normal IO path and
->show_fdinfo():
======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc6-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.2/19710 is trying to acquire lock:
ffff888098ddc450 (sb_writers#4){.+.+}-{0:0}, at: io_write+0x6b5/0xb30 fs/io_uring.c:3296
but task is already holding lock:
ffff8880a11b8428 (&ctx->uring_lock){+.+.}-{3:3}, at: __do_sys_io_uring_enter+0xe9a/0x1bd0 fs/io_uring.c:8348
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&ctx->uring_lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
__io_uring_show_fdinfo fs/io_uring.c:8417 [inline]
io_uring_show_fdinfo+0x194/0xc70 fs/io_uring.c:8460
seq_show+0x4a8/0x700 fs/proc/fd.c:65
seq_read+0x432/0x1070 fs/seq_file.c:208
do_loop_readv_writev fs/read_write.c:734 [inline]
do_loop_readv_writev fs/read_write.c:721 [inline]
do_iter_read+0x48e/0x6e0 fs/read_write.c:955
vfs_readv+0xe5/0x150 fs/read_write.c:1073
kernel_readv fs/splice.c:355 [inline]
default_file_splice_read.constprop.0+0x4e6/0x9e0 fs/splice.c:412
do_splice_to+0x137/0x170 fs/splice.c:871
splice_direct_to_actor+0x307/0x980 fs/splice.c:950
do_splice_direct+0x1b3/0x280 fs/splice.c:1059
do_sendfile+0x55f/0xd40 fs/read_write.c:1540
__do_sys_sendfile64 fs/read_write.c:1601 [inline]
__se_sys_sendfile64 fs/read_write.c:1587 [inline]
__x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1587
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #1 (&p->lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:956 [inline]
__mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
seq_read+0x61/0x1070 fs/seq_file.c:155
pde_read fs/proc/inode.c:306 [inline]
proc_reg_read+0x221/0x300 fs/proc/inode.c:318
do_loop_readv_writev fs/read_write.c:734 [inline]
do_loop_readv_writev fs/read_write.c:721 [inline]
do_iter_read+0x48e/0x6e0 fs/read_write.c:955
vfs_readv+0xe5/0x150 fs/read_write.c:1073
kernel_readv fs/splice.c:355 [inline]
default_file_splice_read.constprop.0+0x4e6/0x9e0 fs/splice.c:412
do_splice_to+0x137/0x170 fs/splice.c:871
splice_direct_to_actor+0x307/0x980 fs/splice.c:950
do_splice_direct+0x1b3/0x280 fs/splice.c:1059
do_sendfile+0x55f/0xd40 fs/read_write.c:1540
__do_sys_sendfile64 fs/read_write.c:1601 [inline]
__se_sys_sendfile64 fs/read_write.c:1587 [inline]
__x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1587
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
-> #0 (sb_writers#4){.+.+}-{0:0}:
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a96/0x5780 kernel/locking/lockdep.c:4441
lock_acquire+0x1f3/0xaf0 kernel/locking/lockdep.c:5029
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write+0x228/0x450 fs/super.c:1672
io_write+0x6b5/0xb30 fs/io_uring.c:3296
io_issue_sqe+0x18f/0x5c50 fs/io_uring.c:5719
__io_queue_sqe+0x280/0x1160 fs/io_uring.c:6175
io_queue_sqe+0x692/0xfa0 fs/io_uring.c:6254
io_submit_sqe fs/io_uring.c:6324 [inline]
io_submit_sqes+0x1761/0x2400 fs/io_uring.c:6521
__do_sys_io_uring_enter+0xeac/0x1bd0 fs/io_uring.c:8349
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
other info that might help us debug this:
Chain exists of:
sb_writers#4 --> &p->lock --> &ctx->uring_lock
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&ctx->uring_lock);
lock(&p->lock);
lock(&ctx->uring_lock);
lock(sb_writers#4);
*** DEADLOCK ***
1 lock held by syz-executor.2/19710:
#0:
ffff8880a11b8428 (&ctx->uring_lock){+.+.}-{3:3}, at: __do_sys_io_uring_enter+0xe9a/0x1bd0 fs/io_uring.c:8348
stack backtrace:
CPU: 0 PID: 19710 Comm: syz-executor.2 Not tainted 5.9.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x198/0x1fd lib/dump_stack.c:118
check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
check_prev_add kernel/locking/lockdep.c:2496 [inline]
check_prevs_add kernel/locking/lockdep.c:2601 [inline]
validate_chain kernel/locking/lockdep.c:3218 [inline]
__lock_acquire+0x2a96/0x5780 kernel/locking/lockdep.c:4441
lock_acquire+0x1f3/0xaf0 kernel/locking/lockdep.c:5029
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write+0x228/0x450 fs/super.c:1672
io_write+0x6b5/0xb30 fs/io_uring.c:3296
io_issue_sqe+0x18f/0x5c50 fs/io_uring.c:5719
__io_queue_sqe+0x280/0x1160 fs/io_uring.c:6175
io_queue_sqe+0x692/0xfa0 fs/io_uring.c:6254
io_submit_sqe fs/io_uring.c:6324 [inline]
io_submit_sqes+0x1761/0x2400 fs/io_uring.c:6521
__do_sys_io_uring_enter+0xeac/0x1bd0 fs/io_uring.c:8349
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45e179
Code: 3d b2 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 0b b2 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:
00007f1194e74c78 EFLAGS:
00000246 ORIG_RAX:
00000000000001aa
RAX:
ffffffffffffffda RBX:
00000000000082c0 RCX:
000000000045e179
RDX:
0000000000000000 RSI:
0000000000000001 RDI:
0000000000000004
RBP:
000000000118cf98 R08:
0000000000000000 R09:
0000000000000000
R10:
0000000000000000 R11:
0000000000000246 R12:
000000000118cf4c
R13:
00007ffd1aa5756f R14:
00007f1194e759c0 R15:
000000000118cf4c
Fix this by just not diving into details if we fail to trylock the
io_uring mutex. We know the ctx isn't going away during this operation,
but we cannot safely iterate buffers/files/personalities if we don't
hold the io_uring mutex.
Reported-by: syzbot+2f8fa4e860edc3066aba@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
projects / kernel.git / commit