During execution of vfs_fsconfig_locked function we can get ERESTARTNOINTR error (or other interrupt error). But we changing fs context fc->phase field to transient states and our entry fc->phase checks in switch cases (see FS_CONTEXT_CREATE_PARAMS, FS_CONTEXT_RECONF_PARAMS) will always fail after syscall restart which will lead to returning -EBUSY to the userspace.
The idea of the fix is to save entry-time fs_context phase field value and recover fc->phase value to the original one before exiting with "interrupt error" (ERESTARTNOINTR or similar). Many thanks to Andrei Vagin <[email protected]> for help with that. Signed-off-by: Alexander Mikhalitsyn <[email protected]> --- fs/fsopen.c | 32 +++++++++++++++++++++++++++++++- 1 file changed, 31 insertions(+), 1 deletion(-) diff --git a/fs/fsopen.c b/fs/fsopen.c index 27a890aa493a..70e6d163c169 100644 --- a/fs/fsopen.c +++ b/fs/fsopen.c @@ -209,6 +209,18 @@ SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags return ret; } +static inline bool is_interrupt_error(int error) +{ + switch (error) { + case -EINTR: + case -ERESTARTSYS: + case -ERESTARTNOHAND: + case -ERESTARTNOINTR: + return true; + } + return false; +} + /* * Check the state and apply the configuration. Note that this function is * allowed to 'steal' the value by setting param->xxx to NULL before returning. @@ -217,11 +229,20 @@ static int vfs_fsconfig_locked(struct fs_context *fc, int cmd, struct fs_parameter *param) { struct super_block *sb; + enum fs_context_phase entry_phase; int ret; ret = finish_clean_context(fc); if (ret) return ret; + + /* We changing fc->phase in the code below but we need to + * return fc->phase to the original value if we get + * "interrupt error" during the process to make fsconfig + * syscall restart procedure work correctly. + */ + entry_phase = fc->phase; + switch (cmd) { case FSCONFIG_CMD_CREATE: if (fc->phase != FS_CONTEXT_CREATE_PARAMS) @@ -264,7 +285,16 @@ static int vfs_fsconfig_locked(struct fs_context *fc, int cmd, return vfs_parse_fs_param(fc, param); } - fc->phase = FS_CONTEXT_FAILED; + + /* We should fail context only if we get real error. + * If we get ERESTARTNOINTR we can safely restart + * fsconfig syscall. + */ + if (is_interrupt_error(ret)) + fc->phase = entry_phase; + else + fc->phase = FS_CONTEXT_FAILED; + return ret; } -- 2.25.1
