Hi Jan,
It seems the new mapping invalidate_lock causes a potential deadlock with
fscache (see attached trace), though the system didn't actually deadlock.
It's quite possible that it's actually a false positive, since chain #1 below
is holding locks in two different filesystems.
Note that this was with my fscache-iter-2 branch, but the I/O paths in use are
mostly upstream and not much affected by that.
This was found whilst running xfstests over afs with a cache, and I'd reached
generic/346 when it tripped, so it seems to happen under very specific
circumstances. Rerunning generic/346 by itself does reproduce the problem.
I'm wondering if I'm going to need to offload netfs_rreq_do_write_to_cache(),
which initiates the write to the cache, to a worker thread.
David
---
WARNING: possible circular locking dependency detected
5.15.0-rc1-build2+ #292 Not tainted
------------------------------------------------------
holetest/65517 is trying to acquire lock:
ffff88810c81d730 (mapping.invalidate_lock#3){.+.+}-{3:3}, at: filemap_fault+0x276/0x7a5
but task is already holding lock:
ffff8881595b53e8 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x28d/0x59c
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&mm->mmap_lock#2){++++}-{3:3}:
validate_chain+0x3c4/0x4a8
__lock_acquire+0x89d/0x949
lock_acquire+0x2dc/0x34b
__might_fault+0x87/0xb1
strncpy_from_user+0x25/0x18c
removexattr+0x7c/0xe5
__do_sys_fremovexattr+0x73/0x96
do_syscall_64+0x67/0x7a
entry_SYSCALL_64_after_hwframe+0x44/0xae
-> #1 (sb_writers#10){.+.+}-{0:0}:
validate_chain+0x3c4/0x4a8
__lock_acquire+0x89d/0x949
lock_acquire+0x2dc/0x34b
cachefiles_write+0x2b3/0x4bb
netfs_rreq_do_write_to_cache+0x3b5/0x432
netfs_readpage+0x2de/0x39d
filemap_read_page+0x51/0x94
filemap_get_pages+0x26f/0x413
filemap_read+0x182/0x427
new_sync_read+0xf0/0x161
vfs_read+0x118/0x16e
ksys_read+0xb8/0x12e
do_syscall_64+0x67/0x7a
entry_SYSCALL_64_after_hwframe+0x44/0xae
-> #0 (mapping.invalidate_lock#3){.+.+}-{3:3}:
check_noncircular+0xe4/0x129
check_prev_add+0x16b/0x3a4
validate_chain+0x3c4/0x4a8
__lock_acquire+0x89d/0x949
lock_acquire+0x2dc/0x34b
down_read+0x40/0x4a
filemap_fault+0x276/0x7a5
__do_fault+0x96/0xbf
do_fault+0x262/0x35a
__handle_mm_fault+0x171/0x1b5
handle_mm_fault+0x12a/0x233
do_user_addr_fault+0x3d2/0x59c
exc_page_fault+0x85/0xa5
asm_exc_page_fault+0x1e/0x30
other info that might help us debug this:
Chain exists of:
mapping.invalidate_lock#3 --> sb_writers#10 --> &mm->mmap_lock#2
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&mm->mmap_lock#2);
lock(sb_writers#10);
lock(&mm->mmap_lock#2);
lock(mapping.invalidate_lock#3);
*** DEADLOCK ***
1 lock held by holetest/65517:
#0: ffff8881595b53e8 (&mm->mmap_lock#2){++++}-{3:3}, at: do_user_addr_fault+0x28d/0x59c
stack backtrace:
CPU: 0 PID: 65517 Comm: holetest Not tainted 5.15.0-rc1-build2+ #292
Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
Call Trace:
dump_stack_lvl+0x45/0x59
check_noncircular+0xe4/0x129
? print_circular_bug+0x207/0x207
? validate_chain+0x461/0x4a8
? add_chain_block+0x88/0xd9
? hlist_add_head_rcu+0x49/0x53
check_prev_add+0x16b/0x3a4
validate_chain+0x3c4/0x4a8
? check_prev_add+0x3a4/0x3a4
? mark_lock+0xa5/0x1c6
__lock_acquire+0x89d/0x949
lock_acquire+0x2dc/0x34b
? filemap_fault+0x276/0x7a5
? rcu_read_unlock+0x59/0x59
? add_to_page_cache_lru+0x13c/0x13c
? lock_is_held_type+0x7b/0xd3
down_read+0x40/0x4a
? filemap_fault+0x276/0x7a5
filemap_fault+0x276/0x7a5
? pagecache_get_page+0x2dd/0x2dd
? __lock_acquire+0x8bc/0x949
? pte_offset_kernel.isra.0+0x6d/0xc3
__do_fault+0x96/0xbf
? do_fault+0x124/0x35a
do_fault+0x262/0x35a
? handle_pte_fault+0x1c1/0x20d
__handle_mm_fault+0x171/0x1b5
? handle_pte_fault+0x20d/0x20d
? __lock_release+0x151/0x254
? mark_held_locks+0x1f/0x78
? rcu_read_unlock+0x3a/0x59
handle_mm_fault+0x12a/0x233
do_user_addr_fault+0x3d2/0x59c
? pgtable_bad+0x70/0x70
? rcu_read_lock_bh_held+0xab/0xab
exc_page_fault+0x85/0xa5
? asm_exc_page_fault+0x8/0x30
asm_exc_page_fault+0x1e/0x30
RIP: 0033:0x40192f
Code: ff 48 89 c3 48 8b 05 50 28 00 00 48 85 ed 7e 23 31 d2 4b 8d 0c 2f eb 0a 0f 1f 00 48 8b 05 39 28 00 00 48 0f af c2 48 83 c2 01 <48> 89 1c 01 48 39 d5 7f e8 8b 0d f2 27 00 00 31 c0 85 c9 74 0e 8b
RSP: 002b:00007f9931867eb0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 00007f9931868700 RCX: 00007f993206ac00
RDX: 0000000000000001 RSI: 0000000000000000 RDI: 00007ffc13e06ee0
RBP: 0000000000000100 R08: 0000000000000000 R09: 00007f9931868700
R10: 00007f99318689d0 R11: 0000000000000202 R12: 00007ffc13e06ee0
R13: 0000000000000c00 R14: 00007ffc13e06e00 R15: 00007f993206a000
