From: "Darrick J. Wong" djwong@kernel.org
mainline-inclusion from mainline-v5.11-rc4 commit 9febcda6f8d1db9f922945d026bb838864b1b6d5 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I4KIAO CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Brian Foster reported a lockdep warning on xfs/167: Reviewed-by: Zhang Yi yi.zhang@huawei.com
============================================ 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://lore.kernel.org/linux-xfs/161142798066.2171939.9311024588681972086.s...
Fixes: a1a7d05a0576 ("xfs: flush speculative space allocations when we run out of space") Reported-by: Brian Foster bfoster@redhat.com Signed-off-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Brian Foster bfoster@redhat.com Reviewed-by: Allison Henderson allison.henderson@oracle.com Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Lihong Kou koulihong@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- 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 3a628c2ea8ac..b2d74a22b231 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);