On 2/19/21 10:23 AM, Darrick J. Wong wrote:
From: Darrick J. Wong <djwong@xxxxxxxxxx>
Brian Foster reported a lockdep warning on xfs/167:
============================================
WARNING: possible recursive locking detected
5.11.0-rc4 #35 Tainted: G W I
--------------------------------------------
fsstress/17733 is trying to acquire lock:
ffff8e0fd1d90650 (sb_internal){++++}-{0:0}, at: xfs_free_eofblocks+0x104/0x1d0 [xfs]
but task is already holding lock:
ffff8e0fd1d90650 (sb_internal){++++}-{0:0}, at: xfs_trans_alloc_inode+0x5f/0x160 [xfs]
stack backtrace:
CPU: 38 PID: 17733 Comm: fsstress Tainted: G W I 5.11.0-rc4 #35
Hardware name: Dell Inc. PowerEdge R740/01KPX8, BIOS 1.6.11 11/20/2018
Call Trace:
dump_stack+0x8b/0xb0
__lock_acquire.cold+0x159/0x2ab
lock_acquire+0x116/0x370
xfs_trans_alloc+0x1ad/0x310 [xfs]
xfs_free_eofblocks+0x104/0x1d0 [xfs]
xfs_blockgc_scan_inode+0x24/0x60 [xfs]
xfs_inode_walk_ag+0x202/0x4b0 [xfs]
xfs_inode_walk+0x66/0xc0 [xfs]
xfs_trans_alloc+0x160/0x310 [xfs]
xfs_trans_alloc_inode+0x5f/0x160 [xfs]
xfs_alloc_file_space+0x105/0x300 [xfs]
xfs_file_fallocate+0x270/0x460 [xfs]
vfs_fallocate+0x14d/0x3d0
__x64_sys_fallocate+0x3e/0x70
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
The cause of this is the new code that spurs a scan to garbage collect
speculative preallocations if we fail to reserve enough blocks while
allocating a transaction. While the warning itself is a fairly benign
lockdep complaint, it does expose a potential livelock if the rwsem
behavior ever changes with regards to nesting read locks when someone's
waiting for a write lock.
Fix this by freeing the transaction and jumping back to xfs_trans_alloc
like this patch in the V4 submission[1].
[1] https://urldefense.com/v3/__https://lore.kernel.org/linux-xfs/161142798066.2171939.9311024588681972086.stgit@magnolia/__;!!GqivPVa7Brio!ONLN-B-M-uqN8aJAN8zMDHDQZ6wwDyF4BSpjkT9j3mV2Zxe5zVD0vgjTWvPFRO2tzEpN$
Fixes: a1a7d05a0576 ("xfs: flush speculative space allocations when we run out of space")
Reported-by: Brian Foster <bfoster@xxxxxxxxxx>
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Ok, makes sense
Reviewed-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
---
v2: fix commit message
---
fs/xfs/xfs_trans.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 44f72c09c203..377f3961d7ed 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -260,6 +260,7 @@ xfs_trans_alloc(
struct xfs_trans **tpp)
{
struct xfs_trans *tp;
+ bool want_retry = true;
int error;
/*
@@ -267,6 +268,7 @@ xfs_trans_alloc(
* GFP_NOFS allocation context so that we avoid lockdep false positives
* by doing GFP_KERNEL allocations inside sb_start_intwrite().
*/
+retry:
tp = kmem_cache_zalloc(xfs_trans_zone, GFP_KERNEL | __GFP_NOFAIL);
if (!(flags & XFS_TRANS_NO_WRITECOUNT))
sb_start_intwrite(mp->m_super);
@@ -289,7 +291,9 @@ xfs_trans_alloc(
tp->t_firstblock = NULLFSBLOCK;
error = xfs_trans_reserve(tp, resp, blocks, rtextents);
- if (error == -ENOSPC) {
+ if (error == -ENOSPC && want_retry) {
+ xfs_trans_cancel(tp);
+
/*
* We weren't able to reserve enough space for the transaction.
* Flush the other speculative space allocations to free space.
@@ -297,8 +301,11 @@ xfs_trans_alloc(
* other locks.
*/
error = xfs_blockgc_free_space(mp, NULL);
- if (!error)
- error = xfs_trans_reserve(tp, resp, blocks, rtextents);
+ if (error)
+ return error;
+
+ want_retry = false;
+ goto retry;
}
if (error) {
xfs_trans_cancel(tp);
