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[193.226.245.188]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c2e31d86372sm177735166b.56.2026.10.01.08.09.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Oct 2026 08:09:39 -0700 (PDT) From: Miklos Szeredi To: fuse-devel@lists.linux.dev Cc: John Groves , John Groves , Amir Goldstein , "Darrick J . Wong" , Vishal Verma , Dave Jiang , Alison Schofield , nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org Subject: [PATCH v2 1/8] dax: replace exported dax_dev_get() with non-allocating dax_dev_find() Date: Thu, 1 Oct 2026 17:07:19 +0200 Message-ID: <20261001150935.655979-2-mszeredi@redhat.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20261001150935.655979-1-mszeredi@redhat.com> References: <20261001150935.655979-1-mszeredi@redhat.com> Precedence: bulk X-Mailing-List: fuse-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: u4HV9VBhd2xWcEjACihaoPmGgtVdh9hjnJFVncDA9sw_1790867381 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true From: John Groves This fix is in response to a Sashiko review, and some subsequent analysis. dax_dev_get() uses iget5_locked() which creates a new inode if no matching one exists. This is correct for the internal caller (alloc_dax), but dangerous for external callers that look up devices from user-supplied or metadata-supplied dev_t values: 1. A new inode is created with DAXDEV_ALIVE set but no backing driver, no ops, and no IDA-allocated minor number. 2. On teardown, dax_destroy_inode() warns because kill_dax() was never called, and dax_free_inode() calls ida_free() for a minor that was never ida_alloc'd -- potentially freeing the minor of a real device. Add dax_dev_find() which uses ilookup5() for lookup-only semantics: it returns an existing dax_device with an elevated inode reference, or NULL if no device with the given dev_t exists. It never creates inodes. A dax_alive() check under dax_read_lock() guards against returning a device that is concurrently being torn down by kill_dax(). Make dax_dev_get() static again (internal to super.c for alloc_dax), export dax_dev_find() instead. Also add the missing CONFIG_DAX=n stub. About the 'fixes' tag: this removes the export of dax_dev_get(), which was flawed, and replaces is with dax_dev_find(). It feels like the fixes tag makes sense for correcting an ABI error. Fixes: 2ae624d5a555d ("dax: export dax_dev_get()") Reviewed-by: Dave Jiang Reviewed-by: Alison Schofield Reviewed-by: "Darrick J. Wong" Signed-off-by: John Groves Signed-off-by: Miklos Szeredi --- drivers/dax/super.c | 38 ++++++++++++++++++++++++++++++++++++-- include/linux/dax.h | 6 +++++- 2 files changed, 41 insertions(+), 3 deletions(-) diff --git a/drivers/dax/super.c b/drivers/dax/super.c index 45f84b0eb909..824e1f6df378 100644 --- a/drivers/dax/super.c +++ b/drivers/dax/super.c @@ -565,7 +565,7 @@ static int dax_set(struct inode *inode, void *data) return 0; } -struct dax_device *dax_dev_get(dev_t devt) +static struct dax_device *dax_dev_get(dev_t devt) { struct dax_device *dax_dev; struct inode *inode; @@ -588,7 +588,41 @@ struct dax_device *dax_dev_get(dev_t devt) return dax_dev; } -EXPORT_SYMBOL_GPL(dax_dev_get); + +/** + * dax_dev_find - look up an existing dax_device by dev_t + * @devt: the device number to find + * + * Returns a dax_device with an elevated inode reference, or NULL if no + * device with the given dev_t exists. Unlike dax_dev_get(), this never + * allocates a new inode -- it is safe for external callers that are looking + * up devices from user-supplied or metadata-supplied dev_t values. + * + * Caller must put_dax() the returned device when done. + */ +struct dax_device *dax_dev_find(dev_t devt) +{ + struct dax_device *dax_dev; + struct inode *inode; + int id; + + inode = ilookup5(dax_superblock, hash_32(devt + DAXFS_MAGIC, 31), + dax_test, &devt); + if (!inode) + return NULL; + + dax_dev = to_dax_dev(inode); + id = dax_read_lock(); + if (!dax_alive(dax_dev)) { + dax_read_unlock(id); + iput(inode); + return NULL; + } + dax_read_unlock(id); + + return dax_dev; +} +EXPORT_SYMBOL_GPL(dax_dev_find); struct dax_device *alloc_dax(void *private, const struct dax_operations *ops) { diff --git a/include/linux/dax.h b/include/linux/dax.h index fe6c3ded1b50..29113eb95e72 100644 --- a/include/linux/dax.h +++ b/include/linux/dax.h @@ -54,7 +54,7 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops); void *dax_holder(struct dax_device *dax_dev); void put_dax(struct dax_device *dax_dev); void kill_dax(struct dax_device *dax_dev); -struct dax_device *dax_dev_get(dev_t devt); +struct dax_device *dax_dev_find(dev_t devt); void dax_write_cache(struct dax_device *dax_dev, bool wc); bool dax_write_cache_enabled(struct dax_device *dax_dev); bool dax_synchronous(struct dax_device *dax_dev); @@ -92,6 +92,10 @@ static inline void put_dax(struct dax_device *dax_dev) static inline void kill_dax(struct dax_device *dax_dev) { } +static inline struct dax_device *dax_dev_find(dev_t devt) +{ + return NULL; +} static inline void dax_write_cache(struct dax_device *dax_dev, bool wc) { } -- 2.54.0