Currently the dma debugging code can end up indirectly calling printk
under the radix_lock. This happens when a radix tree node allocation
fails.
This is a problem because the printk code, when used together with
netconsole, can end up inside the dma debugging code while trying to
transmit a message over netcons.
This creates the possibility of either a circular deadlock on the same
CPU, with that CPU trying to grab the radix_lock twice, or an ABBA
deadlock between different CPUs, where one CPU grabs the console lock
first and then waits for the radix_lock, while the other CPU is holding
the radix_lock and is waiting for the console lock.
The trace captured by lockdep is of the ABBA variant.
-> #2 (&dma_entry_hash[i].lock){-.-.}-{2:2}:
_raw_spin_lock_irqsave+0x5a/0x90
debug_dma_map_page+0x79/0x180
dma_map_page_attrs+0x1d2/0x2f0
bnxt_start_xmit+0x8c6/0x1540
netpoll_start_xmit+0x13f/0x180
netpoll_send_skb+0x20d/0x320
netpoll_send_udp+0x453/0x4a0
write_ext_msg+0x1b9/0x460
console_flush_all+0x2ff/0x5a0
console_unlock+0x55/0x180
vprintk_emit+0x2e3/0x3c0
devkmsg_emit+0x5a/0x80
devkmsg_write+0xfd/0x180
do_iter_readv_writev+0x164/0x1b0
vfs_writev+0xf9/0x2b0
do_writev+0x6d/0x110
do_syscall_64+0x80/0x150
entry_SYSCALL_64_after_hwframe+0x4b/0x53
-> #0 (console_owner){-.-.}-{0:0}:
__lock_acquire+0x15d1/0x31a0
lock_acquire+0xe8/0x290
console_flush_all+0x2ea/0x5a0
console_unlock+0x55/0x180
vprintk_emit+0x2e3/0x3c0
_printk+0x59/0x80
warn_alloc+0x122/0x1b0
__alloc_pages_slowpath+0x1101/0x1120
__alloc_pages+0x1eb/0x2c0
alloc_slab_page+0x5f/0x150
new_slab+0x2dc/0x4e0
___slab_alloc+0xdcb/0x1390
kmem_cache_alloc+0x23d/0x360
radix_tree_node_alloc+0x3c/0xf0
radix_tree_insert+0xf5/0x230
add_dma_entry+0xe9/0x360
dma_map_page_attrs+0x1d2/0x2f0
__bnxt_alloc_rx_frag+0x147/0x180
bnxt_alloc_rx_data+0x79/0x160
bnxt_rx_skb+0x29/0xc0
bnxt_rx_pkt+0xe22/0x1570
__bnxt_poll_work+0x101/0x390
bnxt_poll+0x7e/0x320
__napi_poll+0x29/0x160
net_rx_action+0x1e0/0x3e0
handle_softirqs+0x190/0x510
run_ksoftirqd+0x4e/0x90
smpboot_thread_fn+0x1a8/0x270
kthread+0x102/0x120
ret_from_fork+0x2f/0x40
ret_from_fork_asm+0x11/0x20
This bug is more likely than it seems, because when one CPU has run out
of memory, chances are the other has too.
The good news is, this bug is hidden behind the CONFIG_DMA_API_DEBUG, so
not many users are likely to trigger it.
Signed-off-by: Rik van Riel <riel@surriel.com>
Reported-by: Konstantin Ovsepian <ovs@meta.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
bd44ca3de4