From 16d16e721dbaf9f4bbb6d95503ce32dd007e9680 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Fri, 4 Jul 2025 12:18:02 -0400 Subject: bcachefs: Fix bch2_btree_transactions_read() synchronization Since we're accessing btree_trans objects owned by another thread, we need to guard against using pointers to freed key cache entries: we need our own srcu read lock, and we should skip a btree_trans if it didn't hold the srcu lock (and thus it might have pointers to freed key cache entries). 00693 Mem abort info: 00693 ESR = 0x0000000096000005 00693 EC = 0x25: DABT (current EL), IL = 32 bits 00693 SET = 0, FnV = 0 00693 EA = 0, S1PTW = 0 00693 FSC = 0x05: level 1 translation fault 00693 Data abort info: 00693 ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000 00693 CM = 0, WnR = 0, TnD = 0, TagAccess = 0 00693 GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 00693 user pgtable: 4k pages, 39-bit VAs, pgdp=000000012e650000 00693 [000000008fb96218] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000 00693 Internal error: Oops: 0000000096000005 [#1] SMP 00693 Modules linked in: 00693 CPU: 0 UID: 0 PID: 4307 Comm: cat Not tainted 6.16.0-rc2-ktest-g9e15af94fd86 #27578 NONE 00693 Hardware name: linux,dummy-virt (DT) 00693 pstate: 60001005 (nZCv daif -PAN -UAO -TCO -DIT +SSBS BTYPE=--) 00693 pc : six_lock_counts+0x20/0xe8 00693 lr : bch2_btree_bkey_cached_common_to_text+0x38/0x130 00693 sp : ffffff80ca98bb60 00693 x29: ffffff80ca98bb60 x28: 000000008fb96200 x27: 0000000000000007 00693 x26: ffffff80eafd06b8 x25: 0000000000000000 x24: ffffffc080d75a60 00693 x23: ffffff80eafd0000 x22: ffffffc080bdfcc0 x21: ffffff80eafd0210 00693 x20: ffffff80c192ff08 x19: 000000008fb96200 x18: 00000000ffffffff 00693 x17: 0000000000000000 x16: 0000000000000000 x15: 00000000ffffffff 00693 x14: 0000000000000000 x13: ffffff80ceb5a29a x12: 20796220646c6568 00693 x11: 72205d3e303c5b20 x10: 0000000000000020 x9 : ffffffc0805fb6b0 00693 x8 : 0000000000000020 x7 : 0000000000000000 x6 : 0000000000000020 00693 x5 : ffffff80ceb5a29c x4 : 0000000000000001 x3 : 000000000000029c 00693 x2 : 0000000000000000 x1 : ffffff80ef66c000 x0 : 000000008fb96200 00693 Call trace: 00693 six_lock_counts+0x20/0xe8 (P) 00693 bch2_btree_bkey_cached_common_to_text+0x38/0x130 00693 bch2_btree_trans_to_text+0x260/0x2a8 00693 bch2_btree_transactions_read+0xac/0x1e8 00693 full_proxy_read+0x74/0xd8 00693 vfs_read+0x90/0x300 00693 ksys_read+0x6c/0x108 00693 __arm64_sys_read+0x20/0x30 00693 invoke_syscall.constprop.0+0x54/0xe8 00693 do_el0_svc+0x44/0xc8 00693 el0_svc+0x18/0x58 00693 el0t_64_sync_handler+0x104/0x130 00693 el0t_64_sync+0x154/0x158 00693 Code: 910003fd f9423c22 f90017e2 d2800002 (f9400c01) 00693 ---[ end trace 0000000000000000 ]--- Signed-off-by: Kent Overstreet --- fs/bcachefs/debug.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/bcachefs/debug.c b/fs/bcachefs/debug.c index 79d64052215c..07c2a0f73cc2 100644 --- a/fs/bcachefs/debug.c +++ b/fs/bcachefs/debug.c @@ -584,6 +584,8 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf, i->ubuf = buf; i->size = size; i->ret = 0; + + int srcu_idx = srcu_read_lock(&c->btree_trans_barrier); restart: seqmutex_lock(&c->btree_trans_lock); list_sort(&c->btree_trans_list, list_ptr_order_cmp); @@ -597,6 +599,11 @@ restart: if (!closure_get_not_zero(&trans->ref)) continue; + if (!trans->srcu_held) { + closure_put(&trans->ref); + continue; + } + u32 seq = seqmutex_unlock(&c->btree_trans_lock); bch2_btree_trans_to_text(&i->buf, trans); @@ -618,6 +625,8 @@ restart: } seqmutex_unlock(&c->btree_trans_lock); unlocked: + srcu_read_unlock(&c->btree_trans_barrier, srcu_idx); + if (i->buf.allocation_failure) ret = -ENOMEM; -- cgit v1.2.3