One long-running 5.11.8 system (yes, I know, an upgrade is overdue) using bcache for almost all its fses just WARN_ONed on me: Aug 29 04:11:47 loom warning: [6083976.304807] WARNING: CPU: 3 PID: 407 at drivers/md/bcache/alloc.c:81 __bch_invalidate_one_bucket+0xcb/0xd1 Aug 29 04:11:47 loom warning: [6083976.313994] Modules linked in: vfat fat Aug 29 04:11:47 loom warning: [6083976.322954] CPU: 3 PID: 407 Comm: bcache_allocato Tainted: G W 5.11.8-00023-g95756d87a72e-dirt y #3 Aug 29 04:11:47 loom warning: [6083976.332178] Hardware name: Intel Corporation S2600CWR/S2600CWR, BIOS SE5C610.86B.01.01.0024.021320181901 02/1 3/2018 Aug 29 04:11:47 loom warning: [6083976.341401] RIP: 0010:__bch_invalidate_one_bucket+0xcb/0xd1 Aug 29 04:11:47 loom warning: [6083976.350445] Code: 7b 44 04 01 0f 83 7b ff ff ff 48 8b 05 3e b0 03 01 48 85 c0 74 0f 48 8b 78 08 4c 89 ea 4c 8 9 e6 e8 3a bd 01 00 e9 5b ff ff ff <0f> 0b eb 87 0f 0b 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 0f Aug 29 04:11:47 loom warning: [6083976.369285] RSP: 0018:ffffa2a080aabe30 EFLAGS: 00010202 Aug 29 04:11:47 loom warning: [6083976.378441] RAX: ffff9cc0875a0000 RBX: ffffa2a080a8a4dc RCX: 0000000000000061 Aug 29 04:11:47 loom warning: [6083976.387617] RDX: ffff9cc0875a0000 RSI: ffffa2a080a8a4dc RDI: ffff9cc080ff4000 Aug 29 04:11:47 loom warning: [6083976.396696] RBP: ffffa2a080aabe48 R08: 0000000000000a63 R09: 00000000000000ff Aug 29 04:11:47 loom warning: [6083976.405776] R10: 00000000000003ff R11: ffffa2a080a88f04 R12: ffff9cc080ff4000 Aug 29 04:11:47 loom warning: [6083976.414893] R13: ffff9cc080ff0000 R14: ffffa2a080a892ac R15: ffff9cc080ff4000 Aug 29 04:11:47 loom warning: [6083976.423978] FS: 0000000000000000(0000) GS:ffff9cdf7f8c0000(0000) knlGS:0000000000000000 Aug 29 04:11:47 loom warning: [6083976.433268] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Aug 29 04:11:47 loom warning: [6083976.442310] CR2: 00007fc4cc1f7500 CR3: 0000000c0560a001 CR4: 00000000003726e0 Aug 29 04:11:47 loom warning: [6083976.451396] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 Aug 29 04:11:47 loom warning: [6083976.460407] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Aug 29 04:11:47 loom warning: [6083976.469429] Call Trace: Aug 29 04:11:47 loom warning: [6083976.478340] bch_invalidate_one_bucket+0x17/0x7a Aug 29 04:11:47 loom warning: [6083976.487254] bch_allocator_thread+0xbfb/0xd43 Aug 29 04:11:47 loom warning: [6083976.496274] kthread+0x12c/0x145 Aug 29 04:11:47 loom warning: [6083976.505118] ? bch_invalidate_one_bucket+0x80/0x7a Aug 29 04:11:47 loom warning: [6083976.514080] ? __kthread_bind_mask+0x70/0x66 Aug 29 04:11:47 loom warning: [6083976.523060] ret_from_fork+0x1f/0x2a Aug 29 04:11:47 loom warning: [6083976.532051] ---[ end trace 0d64a5c236f9bdf8 ]--- I don't know what the implications of this warning are, though the system still seems to be running happily. BUCKET_GC_GEN_MAX is only 96, which seems quite low and quite likely to be hit... ubt I don't know what that constant means so I could be totally wrong. It is notable that the unused % of this cache volume has fallen to only 3%: it's quite likely that this warning was emitted when it finally (after three years or so!) ran out of free space and did its first forced GC. I'm not sure how to tell.
