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fs: add missing fences to I_NEW handling

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Suppose there are 2 CPUs racing inode hash lookup func (say ilookup5())
and unlock_new_inode().

In principle the latter can clear the I_NEW flag before prior stores
into the inode were made visible.

The former can in turn observe I_NEW is cleared and proceed to use the
inode, while possibly reading from not-yet-published areas.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Mateusz Guzik
2025-10-06 01:15:26 +02:00
committed by Christian Brauner
parent 0f607a89af
commit 31e332b911
3 changed files with 16 additions and 0 deletions
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8
fs/inode.c
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@@ -1181,6 +1181,10 @@ void unlock_new_inode(struct inode *inode)
lockdep_annotate_inode_mutex_key(inode);
spin_lock(&inode->i_lock);
WARN_ON(!(inode->i_state & I_NEW));
/*
* Pairs with smp_rmb in wait_on_inode().
*/
smp_wmb();
inode->i_state &= ~I_NEW & ~I_CREATING;
/*
* Pairs with the barrier in prepare_to_wait_event() to make sure
@@ -1198,6 +1202,10 @@ void discard_new_inode(struct inode *inode)
lockdep_annotate_inode_mutex_key(inode);
spin_lock(&inode->i_lock);
WARN_ON(!(inode->i_state & I_NEW));
/*
* Pairs with smp_rmb in wait_on_inode().
*/
smp_wmb();
inode->i_state &= ~I_NEW;
/*
* Pairs with the barrier in prepare_to_wait_event() to make sure