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fs: split out functions to hold writers

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When a mount is marked read-only we set MNT_WRITE_HOLD on it if there
aren't currently any active writers. Split this logic out into simple
helpers that we can use in follow-up patches.

Link: https://lore.kernel.org/r/20210121131959.646623-33-christian.brauner@ubuntu.com
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
Christian Brauner 2021-01-21 14:19:51 +01:00
parent e58ace1a0f
commit fbdc2f6c40
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GPG Key ID: 91C61BC06578DCA2
1 changed files with 18 additions and 6 deletions
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24
fs/namespace.c
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@ -470,10 +470,8 @@ void mnt_drop_write_file(struct file *file)
}
EXPORT_SYMBOL(mnt_drop_write_file);
static int mnt_make_readonly(struct mount *mnt)
static inline int mnt_hold_writers(struct mount *mnt)
{
int ret = 0;
mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
/*
* After storing MNT_WRITE_HOLD, we'll read the counters. This store
@ -498,15 +496,29 @@ static int mnt_make_readonly(struct mount *mnt)
* we're counting up here.
*/
if (mnt_get_writers(mnt) > 0)
ret = -EBUSY;
else
mnt->mnt.mnt_flags |= MNT_READONLY;
return -EBUSY;
return 0;
}
static inline void mnt_unhold_writers(struct mount *mnt)
{
/*
* MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
* that become unheld will see MNT_READONLY.
*/
smp_wmb();
mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
}
static int mnt_make_readonly(struct mount *mnt)
{
int ret;
ret = mnt_hold_writers(mnt);
if (!ret)
mnt->mnt.mnt_flags |= MNT_READONLY;
mnt_unhold_writers(mnt);
return ret;
}