On Thu, Nov 24, 2016 at 11:13:37AM +0000, Filipe Manana wrote:
> On Wed, Nov 23, 2016 at 9:22 PM, Liu Bo <bo.li.liu@xxxxxxxxxx> wrote:
> > Hi,
> >
> > On Wed, Nov 23, 2016 at 06:21:35PM +0100, Stefan Priebe - Profihost AG wrote:
> >> Hi,
> >>
> >> sorry last mail was from the wrong box.
> >>
> >> Am 04.11.2016 um 20:20 schrieb Liu Bo:
> >> > If we have
> >> >
> >> > |0--hole--4095||4096--preallocate--12287|
> >> >
> >> > instead of using preallocated space, a 8K direct write will just
> >> > create a new 8K extent and it'll end up with
> >> >
> >> > |0--new extent--8191||8192--preallocate--12287|
> >> >
> >> > It's because we find a hole em and then go to create a new 8K
> >> > extent directly without adjusting @len.
> >>
> >> after applying that one on top of my 4.4 btrfs branch (includes patches
> >> up to 4.10 / next). i'm getting deadlocks in btrfs.
> >
> > This is really interesting, thanks for the quick testing.
> >
> > After going through the stacks listed below, I think the patch has
> > exposed a bug around BTRFS_I(inode)->dio_sem:
> >
> > 1. Since fsync has acquired inode_lock(), the dio write must be
> > an overwrite within EOF.
> >
> > 2. Lets say the inode size is 16k and it already has a preallocated extent [4k, 8k],
> > then we feed it with a dio write against [0k, 8k], with this patch
> > applied, the write can be splitted into a new extent of [0, 4k] and a
> > fill-write against the preallocated one [4k, 8k],
> >
> > 3.
> > dio fsync
> > ->btrfs_direct_IO btrfs_sync_file
> > ->do_direct_IO
> > ->get_more_blocks() ->inode_lock()
> > ->btrfs_get_blocks_direct() # for [0, 8k] ->btrfs_log_inode()
> > ->btrfs_new_direct_extent() ->btrfs_log_changed_extents()
> > ->btrfs_create_dio_extent()
> > ->down_read(&BTRFS_I(inode)->dio_sem)
> > # dio write is splitted and
> > # em of [0, 4k] is inserted as well as
> > # the ordered extent.
> > ->up_read(&BTRFS_I(inode)->dio_sem)
> > # do_direct_IO tries to collect more pages
> > # before sending them down, so [0, 4k] is not
> > # yet submitted.
> > --------------------------------------------------------------------------------------------------------
> > ->down_write(&BTRFS_I(inode)->dio_sem)
> > # found ordered extent of [0, 4k]
> > # wait for [0, 4k] to finish
> > ->get_more_blocks()
> > ->btrfs_get_blocks_direct() # for [4k, 8k]
> > ->btrfs_create_dio_extent()
> > -> up_read(&BTRFS_I(inode)->dio_sem)
> > # deadlock occurs
> >
> > 4. _Without_ this patch, we could hit the deadlock as well under space pressure,
> > i.e. if we request [0, 8k], but btrfs_reserve_extent() returns only [0, 4k].
> >
> > (Filipe may correct me, cc'd Filipe.)
>
> The analysis is correct Bo.
> Originally to fix races between fsync and direct IO writes there was a
> solution [1, 2] that didn't involve adding a semaphore and relied on
> creating first the ordered extents and then the extent maps only in
> the direct IO write path (we do things in the reverse order everywhere
> else). It worked and was documented in comments but wasn't
> particularly elegant and Josef was not happy because of that, so then
> we added the semaphore and made direct IO write path create the extent
> maps and ordered extents in the same order as everywhere else [3].
>
> So here I can only see 2 simple solutions. Either revert [3] (which
> added the semaphore) or acquire the semaphore at a higher level in
> direct IO write path like this:
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 1f980ef..b2c277d 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -7237,7 +7237,6 @@ static struct extent_map
> *btrfs_create_dio_extent(struct inode *inode,
> struct extent_map *em = NULL;
> int ret;
>
> - down_read(&BTRFS_I(inode)->dio_sem);
> if (type != BTRFS_ORDERED_NOCOW) {
> em = create_pinned_em(inode, start, len, orig_start,
> block_start, block_len, orig_block_len,
> @@ -7256,8 +7255,6 @@ static struct extent_map
> *btrfs_create_dio_extent(struct inode *inode,
> em = ERR_PTR(ret);
> }
> out:
> - up_read(&BTRFS_I(inode)->dio_sem);
> -
> return em;
> }
>
> @@ -8715,11 +8712,14 @@ static ssize_t btrfs_direct_IO(struct kiocb
> *iocb, struct iov_iter *iter)
> wakeup = false;
> }
>
> + if (iov_iter_rw(iter) == WRITE)
> + down_read(&BTRFS_I(inode)->dio_sem);
> ret = __blockdev_direct_IO(iocb, inode,
>
> BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev,
> iter, btrfs_get_blocks_direct, NULL,
> btrfs_submit_direct, flags);
> if (iov_iter_rw(iter) == WRITE) {
> + up_read(&BTRFS_I(inode)->dio_sem);
> current->journal_info = NULL;
> if (ret < 0 && ret != -EIOCBQUEUED) {
> if (dio_data.reserve)
>
>
> Let me know what you think. Thanks.
Hi Filipe,
After going over again fs/direct-io.c, the AIO dio_complete is diffrent from the
'Note that' part in your patch [1], what am I missing?
-------------------------------------------------------------------------
static ssize_t dio_complete(struct dio *dio, ssize_t ret, bool is_async)
{
...
if (!(dio->flags & DIO_SKIP_DIO_COUNT))
inode_dio_end(dio->inode);
if (is_async) {
/*
* generic_write_sync expects ki_pos to have been updated
* already, but the submission path only does this for
* synchronous I/O.
*/
dio->iocb->ki_pos += transferred;
if (dio->op == REQ_OP_WRITE)
ret = generic_write_sync(dio->iocb, transferred);
dio->iocb->ki_complete(dio->iocb, ret, 0);
}
...
}
-------------------------------------------------------------------------
[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=de0ee0edb21fbab4c7afa3e94573ecfebfb0244e
Thanks,
-liubo
>
> [1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=de0ee0edb21fbab4c7afa3e94573ecfebfb0244e
> [2] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=0b901916a00bc7b14ee83cc8e41c3b0d561a8f22
> [3] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af
>
>
> >
> > Thanks,
> >
> > -liubo
> >
> >>
> >> Traces here:
> >> INFO: task btrfs-transacti:604 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> btrfs-transacti D ffff8814e78cbe00 0 604 2 0x00080000
> >> ffff8814e78cbe00 ffff88017367a540 ffff8814e2f88000 ffff8814e78cc000
> >> ffff8814e78cbe38 ffff88123616c510 ffff8814e24c81f0 ffff88153fb0a000
> >> ffff8814e78cbe18 ffffffff816a8425 ffff8814e63165a0 ffff8814e78cbe88
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03751a5>] btrfs_commit_transaction+0x275/0xa50 [btrfs]
> >> [<ffffffffc036fdd6>] transaction_kthread+0x1d6/0x200 [btrfs]
> >> [<ffffffff810a0cbb>] kthread+0xdb/0x100
> >> [<ffffffff816ac84f>] ret_from_fork+0x3f/0x70
> >> DWARF2 unwinder stuck at ret_from_fork+0x3f/0x70
> >>
> >> Leftover inexact backtrace:
> >>
> >> [<ffffffff810a0be0>] ? kthread_park+0x60/0x60
> >> INFO: task mysqld:1977 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> mysqld D ffff88142ef1bcf8 0 1977 1 0x00080000
> >> ffff88142ef1bcf8 ffffffff81e0f500 ffff8814dc2c4a80 ffff88142ef1c000
> >> ffff8814e32ed298 ffff8814e32ed2c0 ffff88110aa9a000 ffff8814e32ed000
> >> ffff88142ef1bd10 ffffffff816a8425 ffff8814e32ed000 ffff88142ef1bd60
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03b38a2>] wait_for_writer+0xa2/0xb0 [btrfs]
> >> [<ffffffffc03bb439>] btrfs_sync_log+0xe9/0xa00 [btrfs]
> >> [<ffffffffc038d1bf>] btrfs_sync_file+0x35f/0x3d0 [btrfs]
> >> [<ffffffff8120055d>] vfs_fsync_range+0x3d/0xb0
> >> [<ffffffff8120062d>] do_fsync+0x3d/0x70
> >> [<ffffffff812008a0>] SyS_fsync+0x10/0x20
> >> [<ffffffff816ac4ee>] entry_SYSCALL_64_fastpath+0x12/0x71
> >> DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x71
> >>
> >> Leftover inexact backtrace:
> >>
> >> INFO: task mysqld:3249 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> mysqld D ffff881475fdfa40 0 3249 1 0x00080000
> >> ffff881475fdfa40 ffff88017367ca80 ffff8814433d2540 ffff881475fe0000
> >> ffff88040da39ba0 0000000000230000 ffff88040da39c20 0000000000238000
> >> ffff881475fdfa58 ffffffff816a8425 0000000000008000 ffff881475fdfb18
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03b4cb7>]
> >> wait_ordered_extents.isra.18.constprop.23+0x147/0x3d0 [btrfs]
> >> [<ffffffffc03b5182>] btrfs_log_changed_extents+0x242/0x610 [btrfs]
> >> [<ffffffffc03ba6a4>] btrfs_log_inode+0x874/0xb80 [btrfs]
> >> [<ffffffffc03bac6c>] btrfs_log_inode_parent+0x22c/0x910 [btrfs]
> >> [<ffffffffc03bc292>] btrfs_log_dentry_safe+0x62/0x80 [btrfs]
> >> [<ffffffffc038d0ec>] btrfs_sync_file+0x28c/0x3d0 [btrfs]
> >> [<ffffffff8120055d>] vfs_fsync_range+0x3d/0xb0
> >> [<ffffffff8120062d>] do_fsync+0x3d/0x70
> >> [<ffffffff812008a0>] SyS_fsync+0x10/0x20
> >> [<ffffffff816ac4ee>] entry_SYSCALL_64_fastpath+0x12/0x71
> >> DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x71
> >>
> >> Leftover inexact backtrace:
> >>
> >> INFO: task mysqld:3250 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> mysqld D ffff881374edb868 0 3250 1 0x00080000
> >> ffff881374edb868 ffff8801736b2540 ffff8814433d4a80 ffff881374edc000
> >> ffff8814e26f81c8 ffff8814e26f81e0 0000000000238000 00000000000a8000
> >> ffff881374edb880 ffffffff816a8425 ffff8814433d4a80 ffff881374edb8d8
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffff816aaffd>] rwsem_down_read_failed+0xed/0x130
> >> [<ffffffff813ce404>] call_rwsem_down_read_failed+0x14/0x30
> >> DWARF2 unwinder stuck at call_rwsem_down_read_failed+0x14/0x30
> >>
> >> Leftover inexact backtrace:
> >>
> >> [<ffffffff816aa5a7>] ? down_read+0x17/0x20
> >> [<ffffffffc0376cc6>] btrfs_create_dio_extent+0x46/0x1e0 [btrfs]
> >> [<ffffffffc0386a68>] btrfs_get_blocks_direct+0x3d8/0x730 [btrfs]
> >> [<ffffffffc0378b2e>] ? btrfs_submit_direct+0x1ce/0x740 [btrfs]
> >> [<ffffffff8120b2c7>] do_blockdev_direct_IO+0x11f7/0x2bc0
> >> [<ffffffffc0386690>] ? btrfs_page_exists_in_range+0xe0/0xe0 [btrfs]
> >> [<ffffffffc0378960>] ? btrfs_getattr+0xa0/0xa0 [btrfs]
> >> [<ffffffff8120ccd3>] __blockdev_direct_IO+0x43/0x50
> >> [<ffffffffc0378960>] ? btrfs_getattr+0xa0/0xa0 [btrfs]
> >> [<ffffffffc0377e11>] btrfs_direct_IO+0x1d1/0x380 [btrfs]
> >> [<ffffffffc0378960>] ? btrfs_getattr+0xa0/0xa0 [btrfs]
> >> [<ffffffff8115656a>] generic_file_direct_write+0xaa/0x170
> >> [<ffffffffc038d4de>] btrfs_file_write_iter+0x2ae/0x560 [btrfs]
> >> [<ffffffff810f73c1>] ? futex_wake+0x81/0x150
> >> [<ffffffff811cedd4>] new_sync_write+0x84/0xb0
> >> [<ffffffff811cee26>] __vfs_write+0x26/0x40
> >> [<ffffffff811cf419>] vfs_write+0xa9/0x190
> >> [<ffffffff810026af>] ? enter_from_user_mode+0x1f/0x50
> >> [<ffffffff811d027b>] SyS_pwrite64+0x6b/0xa0
> >> [<ffffffff81002b20>] ? syscall_return_slowpath+0xb0/0x130
> >> [<ffffffff816ac4ee>] entry_SYSCALL_64_fastpath+0x12/0x71
> >> INFO: task btrfs-transacti:604 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> btrfs-transacti D ffff8814e78cbe00 0 604 2 0x00080000
> >> ffff8814e78cbe00 ffff88017367a540 ffff8814e2f88000 ffff8814e78cc000
> >> ffff8814e78cbe38 ffff88123616c510 ffff8814e24c81f0 ffff88153fb0a000
> >> ffff8814e78cbe18 ffffffff816a8425 ffff8814e63165a0 ffff8814e78cbe88
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03751a5>] btrfs_commit_transaction+0x275/0xa50 [btrfs]
> >> [<ffffffffc036fdd6>] transaction_kthread+0x1d6/0x200 [btrfs]
> >> [<ffffffff810a0cbb>] kthread+0xdb/0x100
> >> [<ffffffff816ac84f>] ret_from_fork+0x3f/0x70
> >> DWARF2 unwinder stuck at ret_from_fork+0x3f/0x70
> >>
> >> Leftover inexact backtrace:
> >>
> >> [<ffffffff810a0be0>] ? kthread_park+0x60/0x60
> >> INFO: task mysqld:1977 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> mysqld D ffff88142ef1bcf8 0 1977 1 0x00080000
> >> ffff88142ef1bcf8 ffffffff81e0f500 ffff8814dc2c4a80 ffff88142ef1c000
> >> ffff8814e32ed298 ffff8814e32ed2c0 ffff88110aa9a000 ffff8814e32ed000
> >> ffff88142ef1bd10 ffffffff816a8425 ffff8814e32ed000 ffff88142ef1bd60
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03b38a2>] wait_for_writer+0xa2/0xb0 [btrfs]
> >> [<ffffffffc03bb439>] btrfs_sync_log+0xe9/0xa00 [btrfs]
> >> [<ffffffffc038d1bf>] btrfs_sync_file+0x35f/0x3d0 [btrfs]
> >> [<ffffffff8120055d>] vfs_fsync_range+0x3d/0xb0
> >> [<ffffffff8120062d>] do_fsync+0x3d/0x70
> >> [<ffffffff812008a0>] SyS_fsync+0x10/0x20
> >> [<ffffffff816ac4ee>] entry_SYSCALL_64_fastpath+0x12/0x71
> >> DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x71
> >>
> >> Leftover inexact backtrace:
> >>
> >> INFO: task mysqld:3249 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> mysqld D ffff881475fdfa40 0 3249 1 0x00080000
> >> ffff881475fdfa40 ffff88017367ca80 ffff8814433d2540 ffff881475fe0000
> >> ffff88040da39ba0 0000000000230000 ffff88040da39c20 0000000000238000
> >> ffff881475fdfa58 ffffffff816a8425 0000000000008000 ffff881475fdfb18
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03b4cb7>]
> >> wait_ordered_extents.isra.18.constprop.23+0x147/0x3d0 [btrfs]
> >> [<ffffffffc03b5182>] btrfs_log_changed_extents+0x242/0x610 [btrfs]
> >> [<ffffffffc03ba6a4>] btrfs_log_inode+0x874/0xb80 [btrfs]
> >> [<ffffffffc03bac6c>] btrfs_log_inode_parent+0x22c/0x910 [btrfs]
> >> [<ffffffffc03bc292>] btrfs_log_dentry_safe+0x62/0x80 [btrfs]
> >> [<ffffffffc038d0ec>] btrfs_sync_file+0x28c/0x3d0 [btrfs]
> >> [<ffffffff8120055d>] vfs_fsync_range+0x3d/0xb0
> >> [<ffffffff8120062d>] do_fsync+0x3d/0x70
> >> [<ffffffff812008a0>] SyS_fsync+0x10/0x20
> >> [<ffffffff816ac4ee>] entry_SYSCALL_64_fastpath+0x12/0x71
> >> DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x71
> >>
> >> Leftover inexact backtrace:
> >>
> >> INFO: task mysqld:3250 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> mysqld D ffff881374edb868 0 3250 1 0x00080000
> >> ffff881374edb868 ffff8801736b2540 ffff8814433d4a80 ffff881374edc000
> >> ffff8814e26f81c8 ffff8814e26f81e0 0000000000238000 00000000000a8000
> >> ffff881374edb880 ffffffff816a8425 ffff8814433d4a80 ffff881374edb8d8
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffff816aaffd>] rwsem_down_read_failed+0xed/0x130
> >> [<ffffffff813ce404>] call_rwsem_down_read_failed+0x14/0x30
> >> DWARF2 unwinder stuck at call_rwsem_down_read_failed+0x14/0x30
> >>
> >> Leftover inexact backtrace:
> >>
> >> [<ffffffff816aa5a7>] ? down_read+0x17/0x20
> >> [<ffffffffc0376cc6>] btrfs_create_dio_extent+0x46/0x1e0 [btrfs]
> >> [<ffffffffc0386a68>] btrfs_get_blocks_direct+0x3d8/0x730 [btrfs]
> >> [<ffffffffc0378b2e>] ? btrfs_submit_direct+0x1ce/0x740 [btrfs]
> >> [<ffffffff8120b2c7>] do_blockdev_direct_IO+0x11f7/0x2bc0
> >> [<ffffffffc0386690>] ? btrfs_page_exists_in_range+0xe0/0xe0 [btrfs]
> >> [<ffffffffc0378960>] ? btrfs_getattr+0xa0/0xa0 [btrfs]
> >> [<ffffffff8120ccd3>] __blockdev_direct_IO+0x43/0x50
> >> [<ffffffffc0378960>] ? btrfs_getattr+0xa0/0xa0 [btrfs]
> >> [<ffffffffc0377e11>] btrfs_direct_IO+0x1d1/0x380 [btrfs]
> >> [<ffffffffc0378960>] ? btrfs_getattr+0xa0/0xa0 [btrfs]
> >> [<ffffffff8115656a>] generic_file_direct_write+0xaa/0x170
> >> [<ffffffffc038d4de>] btrfs_file_write_iter+0x2ae/0x560 [btrfs]
> >> [<ffffffff810f73c1>] ? futex_wake+0x81/0x150
> >> [<ffffffff811cedd4>] new_sync_write+0x84/0xb0
> >> [<ffffffff811cee26>] __vfs_write+0x26/0x40
> >> [<ffffffff811cf419>] vfs_write+0xa9/0x190
> >> [<ffffffff810026af>] ? enter_from_user_mode+0x1f/0x50
> >> [<ffffffff811d027b>] SyS_pwrite64+0x6b/0xa0
> >> [<ffffffff81002b20>] ? syscall_return_slowpath+0xb0/0x130
> >> [<ffffffff816ac4ee>] entry_SYSCALL_64_fastpath+0x12/0x71
> >> INFO: task btrfs-transacti:604 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> btrfs-transacti D ffff8814e78cbe00 0 604 2 0x00080000
> >> ffff8814e78cbe00 ffff88017367a540 ffff8814e2f88000 ffff8814e78cc000
> >> ffff8814e78cbe38 ffff88123616c510 ffff8814e24c81f0 ffff88153fb0a000
> >> ffff8814e78cbe18 ffffffff816a8425 ffff8814e63165a0 ffff8814e78cbe88
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03751a5>] btrfs_commit_transaction+0x275/0xa50 [btrfs]
> >> [<ffffffffc036fdd6>] transaction_kthread+0x1d6/0x200 [btrfs]
> >> [<ffffffff810a0cbb>] kthread+0xdb/0x100
> >> [<ffffffff816ac84f>] ret_from_fork+0x3f/0x70
> >> DWARF2 unwinder stuck at ret_from_fork+0x3f/0x70
> >>
> >> Leftover inexact backtrace:
> >>
> >> [<ffffffff810a0be0>] ? kthread_park+0x60/0x60
> >> INFO: task mysqld:1977 blocked for more than 120 seconds.
> >> Not tainted 4.4.34 #1
> >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> >> mysqld D ffff88142ef1bcf8 0 1977 1 0x00080000
> >> ffff88142ef1bcf8 ffffffff81e0f500 ffff8814dc2c4a80 ffff88142ef1c000
> >> ffff8814e32ed298 ffff8814e32ed2c0 ffff88110aa9a000 ffff8814e32ed000
> >> ffff88142ef1bd10 ffffffff816a8425 ffff8814e32ed000 ffff88142ef1bd60
> >> Call Trace:
> >> [<ffffffff816a8425>] schedule+0x35/0x80
> >> [<ffffffffc03b38a2>] wait_for_writer+0xa2/0xb0 [btrfs]
> >> [<ffffffffc03bb439>] btrfs_sync_log+0xe9/0xa00 [btrfs]
> >> [<ffffffffc038d1bf>] btrfs_sync_file+0x35f/0x3d0 [btrfs]
> >> [<ffffffff8120055d>] vfs_fsync_range+0x3d/0xb0
> >> [<ffffffff8120062d>] do_fsync+0x3d/0x70
> >> [<ffffffff812008a0>] SyS_fsync+0x10/0x20
> >> [<ffffffff816ac4ee>] entry_SYSCALL_64_fastpath+0x12/0x71
> >> DWARF2 unwinder stuck at entry_SYSCALL_64_fastpath+0x12/0x71
> >>
> >> Leftover inexact backtrace:
> >>
> >> Greets,
> >> Stefan
> >>
> >> >
> >> > Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> >> > Reviewed-by: Chris Mason <clm@xxxxxx>
> >> > ---
> >> > fs/btrfs/inode.c | 8 +++++---
> >> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >> >
> >> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> >> > index 2b790bd..48e9356 100644
> >> > --- a/fs/btrfs/inode.c
> >> > +++ b/fs/btrfs/inode.c
> >> > @@ -7783,10 +7783,12 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> >> > }
> >> >
> >> > /*
> >> > - * this will cow the extent, reset the len in case we changed
> >> > - * it above
> >> > + * this will cow the extent, if em is within [start, len], then
> >> > + * probably we've found a preallocated/existing extent, let's
> >> > + * give it a chance to use preallocated space.
> >> > */
> >> > - len = bh_result->b_size;
> >> > + len = min_t(u64, bh_result->b_size, em->len - (start - em->start));
> >> > + len = ALIGN(len, root->sectorsize);
> >> > free_extent_map(em);
> >> > em = btrfs_new_extent_direct(inode, start, len);
> >> > if (IS_ERR(em)) {
> >> >
>
>
>
> --
> Filipe David Manana,
>
> "People will forget what you said,
> people will forget what you did,
> but people will never forget how you made them feel."
> --
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