From: Su Yue l@damenly.su
commit c41ec4529d3448df8998950d7bada757a1b321cf upstream.
This effectively reverts commit d5c8238849e7 ("btrfs: convert data_seqcount to seqcount_mutex_t").
While running fstests on 32 bits test box, many tests failed because of warnings in dmesg. One of those warnings (btrfs/003):
[66.441317] WARNING: CPU: 6 PID: 9251 at include/linux/seqlock.h:279 btrfs_remove_chunk+0x58b/0x7b0 [btrfs] [66.441446] CPU: 6 PID: 9251 Comm: btrfs Tainted: G O 5.11.0-rc4-custom+ #5 [66.441449] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ArchLinux 1.14.0-1 04/01/2014 [66.441451] EIP: btrfs_remove_chunk+0x58b/0x7b0 [btrfs] [66.441472] EAX: 00000000 EBX: 00000001 ECX: c576070c EDX: c6b15803 [66.441475] ESI: 10000000 EDI: 00000000 EBP: c56fbcfc ESP: c56fbc70 [66.441477] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 EFLAGS: 00010246 [66.441481] CR0: 80050033 CR2: 05c8da20 CR3: 04b20000 CR4: 00350ed0 [66.441485] Call Trace: [66.441510] btrfs_relocate_chunk+0xb1/0x100 [btrfs] [66.441529] ? btrfs_lookup_block_group+0x17/0x20 [btrfs] [66.441562] btrfs_balance+0x8ed/0x13b0 [btrfs] [66.441586] ? btrfs_ioctl_balance+0x333/0x3c0 [btrfs] [66.441619] ? __this_cpu_preempt_check+0xf/0x11 [66.441643] btrfs_ioctl_balance+0x333/0x3c0 [btrfs] [66.441664] ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs] [66.441683] btrfs_ioctl+0x414/0x2ae0 [btrfs] [66.441700] ? __lock_acquire+0x35f/0x2650 [66.441717] ? lockdep_hardirqs_on+0x87/0x120 [66.441720] ? lockdep_hardirqs_on_prepare+0xd0/0x1e0 [66.441724] ? call_rcu+0x2d3/0x530 [66.441731] ? __might_fault+0x41/0x90 [66.441736] ? kvm_sched_clock_read+0x15/0x50 [66.441740] ? sched_clock+0x8/0x10 [66.441745] ? sched_clock_cpu+0x13/0x180 [66.441750] ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs] [66.441750] ? btrfs_ioctl_get_supported_features+0x30/0x30 [btrfs] [66.441768] __ia32_sys_ioctl+0x165/0x8a0 [66.441773] ? __this_cpu_preempt_check+0xf/0x11 [66.441785] ? __might_fault+0x89/0x90 [66.441791] __do_fast_syscall_32+0x54/0x80 [66.441796] do_fast_syscall_32+0x32/0x70 [66.441801] do_SYSENTER_32+0x15/0x20 [66.441805] entry_SYSENTER_32+0x9f/0xf2 [66.441808] EIP: 0xab7b5549 [66.441814] EAX: ffffffda EBX: 00000003 ECX: c4009420 EDX: bfa91f5c [66.441816] ESI: 00000003 EDI: 00000001 EBP: 00000000 ESP: bfa91e98 [66.441818] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000292 [66.441833] irq event stamp: 42579 [66.441835] hardirqs last enabled at (42585): [<c60eb065>] console_unlock+0x495/0x590 [66.441838] hardirqs last disabled at (42590): [<c60eafd5>] console_unlock+0x405/0x590 [66.441840] softirqs last enabled at (41698): [<c601b76c>] call_on_stack+0x1c/0x60 [66.441843] softirqs last disabled at (41681): [<c601b76c>] call_on_stack+0x1c/0x60
======================================================================== btrfs_remove_chunk+0x58b/0x7b0: __seqprop_mutex_assert at linux/./include/linux/seqlock.h:279 (inlined by) btrfs_device_set_bytes_used at linux/fs/btrfs/volumes.h:212 (inlined by) btrfs_remove_chunk at linux/fs/btrfs/volumes.c:2994 ========================================================================
The warning is produced by lockdep_assert_held() in __seqprop_mutex_assert() if CONFIG_LOCKDEP is enabled. And "olumes.c:2994 is btrfs_device_set_bytes_used() with mutex lock fs_info->chunk_mutex held already.
After adding some debug prints, the cause was found that many __alloc_device() are called with NULL @fs_info (during scanning ioctl). Inside the function, btrfs_device_data_ordered_init() is expanded to seqcount_mutex_init(). In this scenario, its second parameter info->chunk_mutex is &NULL->chunk_mutex which equals to offsetof(struct btrfs_fs_info, chunk_mutex) unexpectedly. Thus, seqcount_mutex_init() is called in wrong way. And later btrfs_device_get/set helpers trigger lockdep warnings.
The device and filesystem object lifetimes are different and we'd have to synchronize initialization of the btrfs_device::data_seqcount with the fs_info, possibly using some additional synchronization. It would still not prevent concurrent access to the seqcount lock when it's used for read and initialization.
Commit d5c8238849e7 ("btrfs: convert data_seqcount to seqcount_mutex_t") does not mention a particular problem being fixed so revert should not cause any harm and we'll get the lockdep warning fixed.
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=210139 Reported-by: Erhard F erhard_f@mailbox.org Fixes: d5c8238849e7 ("btrfs: convert data_seqcount to seqcount_mutex_t") CC: stable@vger.kernel.org # 5.10 CC: Davidlohr Bueso dbueso@suse.de Signed-off-by: Su Yue l@damenly.su Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/volumes.c | 2 +- fs/btrfs/volumes.h | 11 ++++++----- 2 files changed, 7 insertions(+), 6 deletions(-)
--- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -431,7 +431,7 @@ static struct btrfs_device *__alloc_devi
atomic_set(&dev->reada_in_flight, 0); atomic_set(&dev->dev_stats_ccnt, 0); - btrfs_device_data_ordered_init(dev, fs_info); + btrfs_device_data_ordered_init(dev); INIT_RADIX_TREE(&dev->reada_zones, GFP_NOFS & ~__GFP_DIRECT_RECLAIM); INIT_RADIX_TREE(&dev->reada_extents, GFP_NOFS & ~__GFP_DIRECT_RECLAIM); extent_io_tree_init(fs_info, &dev->alloc_state, --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -39,10 +39,10 @@ struct btrfs_io_geometry { #if BITS_PER_LONG==32 && defined(CONFIG_SMP) #include <linux/seqlock.h> #define __BTRFS_NEED_DEVICE_DATA_ORDERED -#define btrfs_device_data_ordered_init(device, info) \ - seqcount_mutex_init(&device->data_seqcount, &info->chunk_mutex) +#define btrfs_device_data_ordered_init(device) \ + seqcount_init(&device->data_seqcount) #else -#define btrfs_device_data_ordered_init(device, info) do { } while (0) +#define btrfs_device_data_ordered_init(device) do { } while (0) #endif
#define BTRFS_DEV_STATE_WRITEABLE (0) @@ -72,8 +72,7 @@ struct btrfs_device { blk_status_t last_flush_error;
#ifdef __BTRFS_NEED_DEVICE_DATA_ORDERED - /* A seqcount_t with associated chunk_mutex (for lockdep) */ - seqcount_mutex_t data_seqcount; + seqcount_t data_seqcount; #endif
/* the internal btrfs device id */ @@ -164,9 +163,11 @@ btrfs_device_get_##name(const struct btr static inline void \ btrfs_device_set_##name(struct btrfs_device *dev, u64 size) \ { \ + preempt_disable(); \ write_seqcount_begin(&dev->data_seqcount); \ dev->name = size; \ write_seqcount_end(&dev->data_seqcount); \ + preempt_enable(); \ } #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPTION) #define BTRFS_DEVICE_GETSET_FUNCS(name) \