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debugfs: initialize cancellations earlier

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Tetsuo Handa pointed out that in the (now reverted)
lockdep commit I initialized the data too late. The
same is true for the cancellation data, it must be
initialized before the cmpxchg(), otherwise it may
be done twice and possibly even overwriting data in
there already when there's a race. Fix that, which
also requires destroying the mutex in case we lost
the race.

Fixes: 8c88a47435 ("debugfs: add API to allow debugfs operations cancellation")
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20231221150444.1e47a0377f80.If7e8ba721ba2956f12c6e8405e7d61e154aa7ae7@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johannes Berg 2023-12-21 15:04:45 +01:00 committed by Greg Kroah-Hartman
parent d400543167
commit 159f5bdadc
1 changed files with 4 additions and 2 deletions
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6
fs/debugfs/file.c
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@ -104,12 +104,14 @@ int debugfs_file_get(struct dentry *dentry)
~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
refcount_set(&fsd->active_users, 1);
init_completion(&fsd->active_users_drained);
INIT_LIST_HEAD(&fsd->cancellations);
mutex_init(&fsd->cancellations_mtx);
if (cmpxchg(&dentry->d_fsdata, d_fsd, fsd) != d_fsd) {
mutex_destroy(&fsd->cancellations_mtx);
kfree(fsd);
fsd = READ_ONCE(dentry->d_fsdata);
}
INIT_LIST_HEAD(&fsd->cancellations);
mutex_init(&fsd->cancellations_mtx);
}
/*