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Fri, 21 Aug 2026 11:15:34 -0700 (PDT) From: Michael Liang To: akinobu.mita@gmail.com, akpm@linux-foundation.org Cc: dennis.dalessandro@cornelisnetworks.com, jgg@ziepe.ca, leon@kernel.org, vbabka@kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Michael Liang Subject: [PATCH] fault-inject: fix dentry leak Date: Fri, 21 Aug 2026 12:15:27 -0600 Message-Id: <20260821181527.3271414-1-mliang@purestorage.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit fault_create_debugfs_attr() has always taken an extra dentry reference on the created directory (attr->dname = dget(dir)) so that fail_dump() could print the name via %pd from any context. Nothing anywhere in the tree ever calls dput() on attr->dname. For callers with a matching teardown, that unmatched reference causes one dentry plus its attached inode to leak per fault_create_debugfs_attr / debugfs_remove_recursive cycle. simple_recursive_removal() drops debugfs's own +1 ref on the child dentry, but the dget()'d ref keeps its refcount at 1: the dentry ends up unhashed but pinned, and its inode is never freed. Boot-once callers (mm/failslab, block/blk-core, etc.) leak exactly once at init and never destroy the tree, so the impact there is bounded. But per-lifecycle callers (drivers/nvme, drivers/infiniband/hw/hfi1, drivers/mmc, drivers/iommu/iommufd, drivers/media, drivers/misc, drivers/gpu/drm/msm, drivers/crypto, net/sunrpc) leak on every create/destroy cycle. We observed this in production: an NVMe/RDMA host repeatedly reconnecting to a target that rejected the CRTO Property Get went through ~50 nvme controller create/destroy cycles per second, and dentry and inode_cache grew by ~13k pinned objects per 240 s -- unrecoverable through drop_caches. Byte math matched a per-cycle 1-dentry / 1-inode leak from the "fault_inject" directory dentry. Fix this by not holding any external reference in fault_attr. Embed the directory name as a fixed-size char array (FAULT_ATTR_DNAME_LEN, 64 bytes) inside struct fault_attr, copied by strscpy() at fault_create_debugfs_attr() time. fail_dump() prints it via %s. Advantages of an embedded array over kstrdup() + kfree() paired with a new destroy API: - Zero API footprint. No new export and no caller changes required: callers already own their fault_attr's memory and free it when they are done, and now that suffices. - No allocation on the create path. - fault_create_debugfs_attr() cannot fail from the name-copy step. - No lifetime coupling between attr->dname and debugfs; the string is valid for exactly as long as the containing struct. The 64-byte length accommodates every in-tree caller with generous headroom (the longest current name is "fail_dma_array_full", 19 chars). The user-visible fail_dump() format changes from "name %pd" to "name %s", but the printed content is identical -- %pd on the created directory renders the same string that was passed in as @name. drivers/infiniband/hw/hfi1/fault.c drops a now-invalid "attr.dname = NULL" statement; the surrounding kzalloc() already zero-initialises the array. Fixes: 6adc4a22f20b ("fault-inject: add ratelimit option") Cc: stable@vger.kernel.org Signed-off-by: Michael Liang --- drivers/infiniband/hw/hfi1/fault.c | 1 - include/linux/fault-inject.h | 10 ++++++++-- lib/fault-inject.c | 7 +++++-- 3 files changed, 13 insertions(+), 5 deletions(-) diff --git a/drivers/infiniband/hw/hfi1/fault.c b/drivers/infiniband/hw/hfi1/fault.c index 4ab72ef03ba1..941a0b96590b 100644 --- a/drivers/infiniband/hw/hfi1/fault.c +++ b/drivers/infiniband/hw/hfi1/fault.c @@ -216,7 +216,6 @@ int hfi1_fault_init_debugfs(struct hfi1_ibdev *ibd) ibd->fault->attr.interval = 1; ibd->fault->attr.require_end = ULONG_MAX; ibd->fault->attr.stacktrace_depth = 32; - ibd->fault->attr.dname = NULL; ibd->fault->attr.verbose = 0; ibd->fault->enable = false; ibd->fault->opcode = false; diff --git a/include/linux/fault-inject.h b/include/linux/fault-inject.h index 58fd14c82270..5c74748a53f3 100644 --- a/include/linux/fault-inject.h +++ b/include/linux/fault-inject.h @@ -18,6 +18,13 @@ enum fault_flags { #include #include +/* + * Length of the debugfs directory name embedded in struct fault_attr. + * Chosen to accommodate every in-tree caller of fault_create_debugfs_attr() + * (the longest is "fail_dma_array_full", 19 chars) with generous headroom. + */ +#define FAULT_ATTR_DNAME_LEN 64 + /* * For explanation of the elements of this struct, see * Documentation/fault-injection/fault-injection.rst @@ -37,7 +44,7 @@ struct fault_attr { unsigned long count; struct ratelimit_state ratelimit_state; - struct dentry *dname; + char dname[FAULT_ATTR_DNAME_LEN]; }; #define FAULT_ATTR_INITIALIZER { \ @@ -47,7 +54,6 @@ struct fault_attr { .stacktrace_depth = 32, \ .ratelimit_state = RATELIMIT_STATE_INIT_DISABLED, \ .verbose = 2, \ - .dname = NULL, \ } #define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER diff --git a/lib/fault-inject.c b/lib/fault-inject.c index 999053fa133e..02916ef2761c 100644 --- a/lib/fault-inject.c +++ b/lib/fault-inject.c @@ -5,6 +5,7 @@ #include #include #include +#include #include #include #include @@ -64,7 +65,7 @@ static void fail_dump(struct fault_attr *attr) { if (attr->verbose > 0 && __ratelimit(&attr->ratelimit_state)) { printk(KERN_NOTICE "FAULT_INJECTION: forcing a failure.\n" - "name %pd, interval %lu, probability %lu, " + "name %s, interval %lu, probability %lu, " "space %d, times %d\n", attr->dname, attr->interval, attr->probability, atomic_read(&attr->space), @@ -261,7 +262,9 @@ struct dentry *fault_create_debugfs_attr(const char *name, debugfs_create_xul("reject-end", mode, dir, &attr->reject_end); #endif /* CONFIG_FAULT_INJECTION_STACKTRACE_FILTER */ - attr->dname = dget(dir); + if (strscpy(attr->dname, name, sizeof(attr->dname)) == -E2BIG) + pr_warn("FAULT_INJECTION: name '%s' truncated to '%s'\n", + name, attr->dname); return dir; } EXPORT_SYMBOL_GPL(fault_create_debugfs_attr); -- 2.34.1