6.6-stable review patch. If anyone has any objections, please let me know.
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From: Rik van Riel riel@surriel.com
[ Upstream commit bd44ca3de49cc1badcff7a96010fa2c64f04868c ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/dma/debug.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index 06366acd27b08..e472cc37d7de4 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -415,8 +415,11 @@ static unsigned long long phys_addr(struct dma_debug_entry *entry) * dma_active_cacheline entry to track per event. dma_map_sg(), on the * other hand, consumes a single dma_debug_entry, but inserts 'nents' * entries into the tree. + * + * Use __GFP_NOWARN because the printk from an OOM, to netconsole, could end + * up right back in the DMA debugging code, leading to a deadlock. */ -static RADIX_TREE(dma_active_cacheline, GFP_ATOMIC); +static RADIX_TREE(dma_active_cacheline, GFP_ATOMIC | __GFP_NOWARN); static DEFINE_SPINLOCK(radix_lock); #define ACTIVE_CACHELINE_MAX_OVERLAP ((1 << RADIX_TREE_MAX_TAGS) - 1) #define CACHELINE_PER_PAGE_SHIFT (PAGE_SHIFT - L1_CACHE_SHIFT)