| Message ID | 20200603101827.2824-1-riteshh@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/1] ext4: mballoc: Use raw_cpu_ptr instead of this_cpu_ptr | expand |
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index a9083113a8c0..b79b32dbe3ea 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -4708,7 +4708,7 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle, } ac->ac_op = EXT4_MB_HISTORY_PREALLOC; - seq = *this_cpu_ptr(&discard_pa_seq); + seq = *raw_cpu_ptr(&discard_pa_seq); if (!ext4_mb_use_preallocated(ac)) { ac->ac_op = EXT4_MB_HISTORY_ALLOC; ext4_mb_normalize_request(ac, ar);
It doesn't really matter in ext4_mb_new_blocks() about whether the code is rescheduled on any other cpu due to preemption. Because we care about discard_pa_seq only when the block allocation fails and then too we add the seq counter of all the cpus against the initial sampled one to check if anyone has freed any blocks while we were doing allocation. So just use raw_cpu_ptr instead of this_cpu_ptr to avoid this BUG. BUG: using smp_processor_id() in preemptible [00000000] code: syz-fuzzer/6927 caller is ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711 CPU: 1 PID: 6927 Comm: syz-fuzzer Not tainted 5.7.0-next-20200602-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x18f/0x20d lib/dump_stack.c:118 check_preemption_disabled+0x20d/0x220 lib/smp_processor_id.c:48 ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711 ext4_ext_map_blocks+0x201b/0x33e0 fs/ext4/extents.c:4244 ext4_map_blocks+0x4cb/0x1640 fs/ext4/inode.c:626 ext4_getblk+0xad/0x520 fs/ext4/inode.c:833 ext4_bread+0x7c/0x380 fs/ext4/inode.c:883 ext4_append+0x153/0x360 fs/ext4/namei.c:67 ext4_init_new_dir fs/ext4/namei.c:2757 [inline] ext4_mkdir+0x5e0/0xdf0 fs/ext4/namei.c:2802 vfs_mkdir+0x419/0x690 fs/namei.c:3632 do_mkdirat+0x21e/0x280 fs/namei.c:3655 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359 entry_SYSCALL_64_after_hwframe+0x44/0xa9 Fixes: 42f56b7a4a7d ("ext4: mballoc: introduce pcpu seqcnt for freeing PA to improve ENOSPC handling") Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com> Reported-by: syzbot+82f324bb69744c5f6969@syzkaller.appspotmail.com --- fs/ext4/mballoc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)