[PATCH v2] initramfs: finish fput() before accessing any binary from initramfs

From: Lokesh Vutla
Date: Tue Jan 24 2017 - 00:38:39 EST

commit 4a9d4b024a31 ("switch fput to task_work_add") implements a
schedule_work() for completing fput(), but did not guarantee calling
__fput() after unpacking initramfs. Because of this, there is a
possibility that during boot a driver can see ETXTBSY when it tries
to load a binary from initramfs as fput() is still pending on that
binary. This patch makes sure that fput() is completed after unpacking

Reported-by: Murali Karicheri <m-karicheri2@xxxxxx>
Signed-off-by: Lokesh Vutla <lokeshvutla@xxxxxx>
Link to RFC: https://patchwork.kernel.org/patch/9520539/
Changes since v1:
- Moved flush_delayed_fput() before loading default modules.

Note: Reproduced on TI K2HK EVM. K2HK Queue Manager subsystem driver[1] tries
to load a firmware from initramfs during boot. Sometimes loading of this
firmware fails with error ETXTBSY. Digging a bit more observed that
deny_write_access() is returning ETXTBSY as inode->i_writecount is > 0
for that file. This is because Unpacking initramfs does a
get_write_access(from open) but hasn't done put_write_access(from fput)
as it hasn't been scheduled yet.

[1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/soc/ti/knav_qmss_queue.c

init/initramfs.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/init/initramfs.c b/init/initramfs.c
index b32ad7d97ac9..981f286c1d16 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -18,6 +18,7 @@
#include <linux/dirent.h>
#include <linux/syscalls.h>
#include <linux/utime.h>
+#include <linux/file.h>

static ssize_t __init xwrite(int fd, const char *p, size_t count)
@@ -647,6 +648,7 @@ static int __init populate_rootfs(void)
printk(KERN_EMERG "Initramfs unpacking failed: %s\n", err);
+ flush_delayed_fput();
* Try loading default modules from initramfs. This gives
* us a chance to load before device_initcalls.