* [PATCHv3 0/1] xfs: soft lockups in unmapping and reflink remapping path
@ 2024-05-07 5:13 Ritesh Harjani (IBM)
2024-05-07 5:13 ` [PATCHv3 1/1] xfs: Add cond_resched to xfs_defer_finish_noroll Ritesh Harjani (IBM)
0 siblings, 1 reply; 3+ messages in thread
From: Ritesh Harjani (IBM) @ 2024-05-07 5:13 UTC (permalink / raw
To: linux-xfs
Cc: Dave Chinner, Darrick J . Wong, Christoph Hellwig, Ojaswin Mujoo,
Ritesh Harjani
Hello,
In one of the testcases, parallel async dio writes to a file generates
large no. of extents (upto 2M or more), and then this file is cleaned up for
running other I/O tests. In the process of deleting this file, soft lockup
messages are observed. We believe this is happening due to kernel being busy
in unmapping/freeing those extents as part of the transaction processing.
This is similar observation with the same call stack which was also reported
here [1]. I also tried the qemu-img bench testcase shared in [1], and I was
able to reproduce the soft lockup with that on Power.
Similarly another instance was reported where xfs reflink remapping path also
saw a similar softlockup problem while iterating over deferrd work items
in xfs_trans_commit() -> xfs_defer_finish_noroll().
So as I understood from that discussion [1], that kernel is moving towards a new
preemption model, but IIUC, it is still an ongoing work.
Also IMHO, this is still a problem in upstream and in older stable kernels
which we still do support and such a fix might still be necessary for them.
This patch fixes the softlockup warning for both of the callstacks.
v2 -> v3:
Move cond_resched within xfs_defer_finish_noroll() loop
[v2]: https://lore.kernel.org/linux-xfs/cover.1714033516.git.ritesh.list@gmail.com/
Ritesh Harjani (IBM) (1):
xfs: Add cond_resched to xfs_defer_finish_noroll
fs/xfs/libxfs/xfs_defer.c | 1 +
1 file changed, 1 insertion(+)
--
2.44.0
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCHv3 1/1] xfs: Add cond_resched to xfs_defer_finish_noroll
2024-05-07 5:13 [PATCHv3 0/1] xfs: soft lockups in unmapping and reflink remapping path Ritesh Harjani (IBM)
@ 2024-05-07 5:13 ` Ritesh Harjani (IBM)
2024-05-07 6:06 ` Dave Chinner
0 siblings, 1 reply; 3+ messages in thread
From: Ritesh Harjani (IBM) @ 2024-05-07 5:13 UTC (permalink / raw
To: linux-xfs
Cc: Dave Chinner, Darrick J . Wong, Christoph Hellwig, Ojaswin Mujoo,
Ritesh Harjani
An async dio write to a sparse file can generate a lot of extents
and when we unlink this file (using rm), the kernel can be busy in umapping
and freeing those extents as part of transaction processing.
Similarly xfs reflink remapping path also goes through
xfs_defer_finish_noroll() for transaction processing. Since we can busy loop
in this function, so let's add cond_resched() to avoid softlockup messages
like these.
watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/1:0:82435]
CPU: 1 PID: 82435 Comm: kworker/1:0 Tainted: G S L 6.9.0-rc5-0-default #1
Workqueue: xfs-inodegc/sda2 xfs_inodegc_worker
NIP [c000000000beea10] xfs_extent_busy_trim+0x100/0x290
LR [c000000000bee958] xfs_extent_busy_trim+0x48/0x290
Call Trace:
xfs_alloc_get_rec+0x54/0x1b0 (unreliable)
xfs_alloc_compute_aligned+0x5c/0x144
xfs_alloc_ag_vextent_size+0x238/0x8d4
xfs_alloc_fix_freelist+0x540/0x694
xfs_free_extent_fix_freelist+0x84/0xe0
__xfs_free_extent+0x74/0x1ec
xfs_extent_free_finish_item+0xcc/0x214
xfs_defer_finish_one+0x194/0x388
xfs_defer_finish_noroll+0x1b4/0x5c8
xfs_defer_finish+0x2c/0xc4
xfs_bunmapi_range+0xa4/0x100
xfs_itruncate_extents_flags+0x1b8/0x2f4
xfs_inactive_truncate+0xe0/0x124
xfs_inactive+0x30c/0x3e0
xfs_inodegc_worker+0x140/0x234
process_scheduled_works+0x240/0x57c
worker_thread+0x198/0x468
kthread+0x138/0x140
start_kernel_thread+0x14/0x18
run fstests generic/175 at 2024-02-02 04:40:21
[ C17] watchdog: BUG: soft lockup - CPU#17 stuck for 23s! [xfs_io:7679]
watchdog: BUG: soft lockup - CPU#17 stuck for 23s! [xfs_io:7679]
CPU: 17 PID: 7679 Comm: xfs_io Kdump: loaded Tainted: G X 6.4.0
NIP [c008000005e3ec94] xfs_rmapbt_diff_two_keys+0x54/0xe0 [xfs]
LR [c008000005e08798] xfs_btree_get_leaf_keys+0x110/0x1e0 [xfs]
Call Trace:
0xc000000014107c00 (unreliable)
__xfs_btree_updkeys+0x8c/0x2c0 [xfs]
xfs_btree_update_keys+0x150/0x170 [xfs]
xfs_btree_lshift+0x534/0x660 [xfs]
xfs_btree_make_block_unfull+0x19c/0x240 [xfs]
xfs_btree_insrec+0x4e4/0x630 [xfs]
xfs_btree_insert+0x104/0x2d0 [xfs]
xfs_rmap_insert+0xc4/0x260 [xfs]
xfs_rmap_map_shared+0x228/0x630 [xfs]
xfs_rmap_finish_one+0x2d4/0x350 [xfs]
xfs_rmap_update_finish_item+0x44/0xc0 [xfs]
xfs_defer_finish_noroll+0x2e4/0x740 [xfs]
__xfs_trans_commit+0x1f4/0x400 [xfs]
xfs_reflink_remap_extent+0x2d8/0x650 [xfs]
xfs_reflink_remap_blocks+0x154/0x320 [xfs]
xfs_file_remap_range+0x138/0x3a0 [xfs]
do_clone_file_range+0x11c/0x2f0
vfs_clone_file_range+0x60/0x1c0
ioctl_file_clone+0x78/0x140
sys_ioctl+0x934/0x1270
system_call_exception+0x158/0x320
system_call_vectored_common+0x15c/0x2ec
Cc: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
fs/xfs/libxfs/xfs_defer.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/xfs/libxfs/xfs_defer.c b/fs/xfs/libxfs/xfs_defer.c
index c13276095cc0..cb185b97447d 100644
--- a/fs/xfs/libxfs/xfs_defer.c
+++ b/fs/xfs/libxfs/xfs_defer.c
@@ -705,6 +705,7 @@ xfs_defer_finish_noroll(
error = xfs_defer_finish_one(*tp, dfp);
if (error && error != -EAGAIN)
goto out_shutdown;
+ cond_resched();
}
/* Requeue the paused items in the outgoing transaction. */
--
2.44.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCHv3 1/1] xfs: Add cond_resched to xfs_defer_finish_noroll
2024-05-07 5:13 ` [PATCHv3 1/1] xfs: Add cond_resched to xfs_defer_finish_noroll Ritesh Harjani (IBM)
@ 2024-05-07 6:06 ` Dave Chinner
0 siblings, 0 replies; 3+ messages in thread
From: Dave Chinner @ 2024-05-07 6:06 UTC (permalink / raw
To: Ritesh Harjani (IBM)
Cc: linux-xfs, Darrick J . Wong, Christoph Hellwig, Ojaswin Mujoo
On Tue, May 07, 2024 at 10:43:07AM +0530, Ritesh Harjani (IBM) wrote:
> An async dio write to a sparse file can generate a lot of extents
> and when we unlink this file (using rm), the kernel can be busy in umapping
> and freeing those extents as part of transaction processing.
>
> Similarly xfs reflink remapping path also goes through
> xfs_defer_finish_noroll() for transaction processing. Since we can busy loop
> in this function, so let's add cond_resched() to avoid softlockup messages
> like these.
You proposed this change two weeks ago: I said:
"The problem is the number of extents being processed without
yielding, not the time spent processing each individual deferred
work chain to free the extent. Hence the explicit rescheduling
should be at the top level loop where it can be easily explained and
understand, not hidden deep inside the defer chain mechanism...."
https://lore.kernel.org/linux-xfs/ZiWjbWrD60W%2F0s%2FF@dread.disaster.area/
> watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/1:0:82435]
> CPU: 1 PID: 82435 Comm: kworker/1:0 Tainted: G S L 6.9.0-rc5-0-default #1
> Workqueue: xfs-inodegc/sda2 xfs_inodegc_worker
> NIP [c000000000beea10] xfs_extent_busy_trim+0x100/0x290
> LR [c000000000bee958] xfs_extent_busy_trim+0x48/0x290
> Call Trace:
> xfs_alloc_get_rec+0x54/0x1b0 (unreliable)
> xfs_alloc_compute_aligned+0x5c/0x144
> xfs_alloc_ag_vextent_size+0x238/0x8d4
> xfs_alloc_fix_freelist+0x540/0x694
> xfs_free_extent_fix_freelist+0x84/0xe0
> __xfs_free_extent+0x74/0x1ec
> xfs_extent_free_finish_item+0xcc/0x214
> xfs_defer_finish_one+0x194/0x388
> xfs_defer_finish_noroll+0x1b4/0x5c8
> xfs_defer_finish+0x2c/0xc4
> xfs_bunmapi_range+0xa4/0x100
> xfs_itruncate_extents_flags+0x1b8/0x2f4
> xfs_inactive_truncate+0xe0/0x124
> xfs_inactive+0x30c/0x3e0
This is the same issue as you originally reported two weeks ago. My
comments about it still stand.
> xfs_inodegc_worker+0x140/0x234
> process_scheduled_works+0x240/0x57c
> worker_thread+0x198/0x468
> kthread+0x138/0x140
> start_kernel_thread+0x14/0x18
>
> run fstests generic/175 at 2024-02-02 04:40:21
> [ C17] watchdog: BUG: soft lockup - CPU#17 stuck for 23s! [xfs_io:7679]
> watchdog: BUG: soft lockup - CPU#17 stuck for 23s! [xfs_io:7679]
> CPU: 17 PID: 7679 Comm: xfs_io Kdump: loaded Tainted: G X 6.4.0
> NIP [c008000005e3ec94] xfs_rmapbt_diff_two_keys+0x54/0xe0 [xfs]
> LR [c008000005e08798] xfs_btree_get_leaf_keys+0x110/0x1e0 [xfs]
> Call Trace:
> 0xc000000014107c00 (unreliable)
> __xfs_btree_updkeys+0x8c/0x2c0 [xfs]
> xfs_btree_update_keys+0x150/0x170 [xfs]
> xfs_btree_lshift+0x534/0x660 [xfs]
> xfs_btree_make_block_unfull+0x19c/0x240 [xfs]
> xfs_btree_insrec+0x4e4/0x630 [xfs]
> xfs_btree_insert+0x104/0x2d0 [xfs]
> xfs_rmap_insert+0xc4/0x260 [xfs]
> xfs_rmap_map_shared+0x228/0x630 [xfs]
> xfs_rmap_finish_one+0x2d4/0x350 [xfs]
> xfs_rmap_update_finish_item+0x44/0xc0 [xfs]
> xfs_defer_finish_noroll+0x2e4/0x740 [xfs]
> __xfs_trans_commit+0x1f4/0x400 [xfs]
> xfs_reflink_remap_extent+0x2d8/0x650 [xfs]
> xfs_reflink_remap_blocks+0x154/0x320 [xfs]
And this is the same case of iterating millions of extents without
ever blocking on a lock, a buffer cache miss, transaction
reservation, etc. IOWs, xfs_reflink_remap_blocks() is another high
level extent iterator that needs the cond_resched() calls.
I can't wait for the kernel to always be pre-emptible so this whole
class of nasty hacks can go away forever. But in the mean time, they
still need to be placed appropriately.
-Dave.
--
Dave Chinner
david@fromorbit.com
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2024-05-07 5:13 [PATCHv3 0/1] xfs: soft lockups in unmapping and reflink remapping path Ritesh Harjani (IBM)
2024-05-07 5:13 ` [PATCHv3 1/1] xfs: Add cond_resched to xfs_defer_finish_noroll Ritesh Harjani (IBM)
2024-05-07 6:06 ` Dave Chinner
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