On Fri, Jul 5, 2019 at 10:09 AM Nikolay Borisov <nborisov@xxxxxxxx> wrote:
>
>
>
> On 4.07.19 г. 18:24 ч., fdmanana@xxxxxxxxxx wrote:
> > From: Filipe Manana <fdmanana@xxxxxxxx>
> >
> > If we are able to load an existing inode cache off disk, we set the state
> > of the cache to BTRFS_CACHE_FINISHED, but we don't wake up any one waiting
> > for the cache to be available. This means that anyone waiting for the
> > cache to be available, waiting on the condition that either its state is
> > BTRFS_CACHE_FINISHED or its available free space is greather than zero,
> > can hang forever.
> >
> > This could be observed running fstests with MOUNT_OPTIONS="-o inode_cache",
> > in particular test case generic/161 triggered it very frequently for me,
> > producing a trace like the following:
> >
> > [63795.739712] BTRFS info (device sdc): enabling inode map caching
> > [63795.739714] BTRFS info (device sdc): disk space caching is enabled
> > [63795.739716] BTRFS info (device sdc): has skinny extents
> > [64036.653886] INFO: task btrfs-transacti:3917 blocked for more than 120 seconds.
> > [64036.654079] Not tainted 5.2.0-rc4-btrfs-next-50 #1
> > [64036.654143] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > [64036.654232] btrfs-transacti D 0 3917 2 0x80004000
> > [64036.654239] Call Trace:
> > [64036.654258] ? __schedule+0x3ae/0x7b0
> > [64036.654271] schedule+0x3a/0xb0
> > [64036.654325] btrfs_commit_transaction+0x978/0xae0 [btrfs]
> > [64036.654339] ? remove_wait_queue+0x60/0x60
> > [64036.654395] transaction_kthread+0x146/0x180 [btrfs]
> > [64036.654450] ? btrfs_cleanup_transaction+0x620/0x620 [btrfs]
> > [64036.654456] kthread+0x103/0x140
> > [64036.654464] ? kthread_create_worker_on_cpu+0x70/0x70
> > [64036.654476] ret_from_fork+0x3a/0x50
> > [64036.654504] INFO: task xfs_io:3919 blocked for more than 120 seconds.
> > [64036.654568] Not tainted 5.2.0-rc4-btrfs-next-50 #1
> > [64036.654617] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > [64036.654685] xfs_io D 0 3919 3633 0x00000000
> > [64036.654691] Call Trace:
> > [64036.654703] ? __schedule+0x3ae/0x7b0
> > [64036.654716] schedule+0x3a/0xb0
> > [64036.654756] btrfs_find_free_ino+0xa9/0x120 [btrfs]
> > [64036.654764] ? remove_wait_queue+0x60/0x60
> > [64036.654809] btrfs_create+0x72/0x1f0 [btrfs]
> > [64036.654822] lookup_open+0x6bc/0x790
> > [64036.654849] path_openat+0x3bc/0xc00
> > [64036.654854] ? __lock_acquire+0x331/0x1cb0
> > [64036.654869] do_filp_open+0x99/0x110
> > [64036.654884] ? __alloc_fd+0xee/0x200
> > [64036.654895] ? do_raw_spin_unlock+0x49/0xc0
> > [64036.654909] ? do_sys_open+0x132/0x220
> > [64036.654913] do_sys_open+0x132/0x220
> > [64036.654926] do_syscall_64+0x60/0x1d0
> > [64036.654933] entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > Fix this by adding a wake_up() call right after setting the cache state to
> > BTRFS_CACHE_FINISHED, at start_caching(), when we are able to load the
> > cache from disk.
> >
> > Fixes: 82d5902d9c681b ("Btrfs: Support reading/writing on disk free ino cache")
> > Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
>
> Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
> > ---
> > fs/btrfs/inode-map.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
> > index ffca2abf13d0..4a5882665f8a 100644
> > --- a/fs/btrfs/inode-map.c
> > +++ b/fs/btrfs/inode-map.c
> > @@ -145,6 +145,7 @@ static void start_caching(struct btrfs_root *root)
> > spin_lock(&root->ino_cache_lock);
> > root->ino_cache_state = BTRFS_CACHE_FINISHED;
> > spin_unlock(&root->ino_cache_lock);
> > + wake_up(&root->ino_cache_wait);
>
> One of the two callers of start_caching doesn't actually wait for the
> cache to load - btrfs_return_ino. Is this expected or is it also a bug?
It's expected. It doesn't need to allocate an inode, so it doesn't
need to wait for the caching to complete - it just wants to mark an
inode as free in the cache.
>
> The presence of such a glaring omission of the wake up means this code
> hasn't been tested much.
It hasn't. Last time I tried it was more than one year ago, maybe two.
Thanks.
>
> > return;
> > }
> >
> >
