btrfs-convert sometimes show 'Assertion failed' in converting a nearly blank
file system, as:
create btrfs filesystem:
blocksize: 4096
nodesize: 16384
features: extref, skinny-metadata (default)
creating btrfs metadata.
creating ext2fs image file.
trans 7 running 5
ctree.c:363: btrfs_cow_block: Assertion `1` failed.
btrfs-convert(btrfs_cow_block+0x92)[0x40acaf]
btrfs-convert(btrfs_search_slot+0x1cb)[0x40c50f]
btrfs-convert(btrfs_csum_file_block+0x20f)[0x41d83a]
btrfs-convert[0x43422d]
btrfs-convert[0x4342cd]
btrfs-convert[0x4345ca]
btrfs-convert[0x434767]
btrfs-convert[0x435770]
btrfs-convert[0x439748]
btrfs-convert(main+0x13f8)[0x43b09d]
/lib64/libc.so.6(__libc_start_main+0xfd)[0x335e01ecdd]
btrfs-convert[0x407649]
Reason is complex:
1: main thread allocated a block of memory,
shared with sub thread
2: main thread killed sub thread, and free above memory
3: main thread malloc a new one(in same address),
and use it
4: sub thread(which is not really quit), write into
this address, and caused this bug.
By adding some debug lines into code, we can see following output:
create btrfs filesystem:
blocksize: 4096
nodesize: 16384
features: extref, skinny-metadata (default)
creating btrfs metadata.
1: ctx(0x7ffe1abde230)->info=0xc65b80
2: task_period_start: will create periodic.timer_fd
3: task_stop: info->periodic.timer_fd = NULL
4: task_stop: begin pthread_cancel info->id=-1746053376
5: task_stop: done pthread_cancel ret=0
6: task_stop: begin info->postfn
7: task_period_stop: periodic.timer_fd NULL
8: task_stop: done info->postfn
9: task_stop: done all
10: creating ext2fs image file.
trans 7 running 5
11: task_period_start: create periodic.timer_fd done info->periodic.timer_fd(0xc65b80)=7
12: btrfs_cow_block: root->fs_info->generation(0xc63568) = 5 trans->transid(0xc65b80)=7
13: ctree.c:368: btrfs_cow_block: Assertion `1` failed.
./btrfs-convert(btrfs_cow_block+0xda)[0x40ad37]
./btrfs-convert(btrfs_search_slot+0x1cb)[0x40c5b4]
./btrfs-convert(btrfs_insert_empty_items+0xac)[0x40d9f6]
./btrfs-convert(btrfs_record_file_extent+0xc0)[0x4183fe]
./btrfs-convert[0x435796]
./btrfs-convert[0x439b0c]
./btrfs-convert(main+0x13f8)[0x43b45d]
/lib64/libc.so.6(__libc_start_main+0xfd)[0x335e01ecdd]
./btrfs-convert[0x407689]
Conclusion:
a: subthread should exit before step 5, but it is still running
in step 11
b: task_stop() hadn't close periodic.timer_fd in step3,
because periodic.timer_fd is not initialized yet.
c. address of 0xc65b80 is overwrited by subthread in step 11,
but this address is freed and re-malloc by main thread
before step 10, and used for trans->transid.
d: trans->transid which is overwrite by subthread caused error
in step 13.
Fix:
pthread_cancel() only send a cancellation request to the thread,
thread will quit in next cancellation point by default.
To make sub thread quit in time, this patch add pthread_join()
after pthread_cancel() call.
And to make pthread_join() works, pthread_detach() is removed.
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
73e211a7a8