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	Sun, 13 Sep 2026 22:42:23 +0000
Date: Sun, 13 Sep 2026 23:42:23 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Mikko Rantalainen <mikko.rantalainen@peda.net>
Cc: linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org, brauner@kernel.org,
	viro@zeniv.linux.org.uk, jack@suse.cz, alx@kernel.org,
	dalias@libc.org
Subject: Re: [RFC PATCH 0/1] close(): stop exposing non-retryable EINTR
Message-ID: <aqcmz5uI7PgN5CT7@casper.infradead.org>
References: <20260913193815.2862366-1-mikko.rantalainen@peda.net>
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In-Reply-To: <20260913193815.2862366-1-mikko.rantalainen@peda.net>

On Sun, Sep 13, 2026 at 10:38:14PM +0300, Mikko Rantalainen wrote:
> However, currently Linux kernel will return EINTR in some cases for
> close(). There is no good way for caller to recover from this case using
> the original fd. Whatever action was actually interrupted cannot be
> resumed or retried through this fd, because the fd has already been
> consumed. Even worse, EINTR conventionally invites retrying an operation,
> but retrying close() is unsafe: the same file descriptor number may
> already refer to another file opened by another thread by the time
> close() returns EINTR.
> 
> In addition, POSIX.1-2024 requires that if close() reports EINTR, the
> descriptor must remain open. It also explicitly permits an interrupted
> close() to return success after closing the descriptor.

I think any filesystem / device driver / ... which returns -EINTR from
close() is broken.  There is one exception though -- if the signal is
fatal.  It's like read()/write() being killable; if the signal is fatal,
the task dies before it gets to see the errno.  So it doesn't matter.

So that's my preferred solution; track down the bad kernel code that's
doing things in close() that are "interruptible" and convert them to
"killable".  We don't want SIGWINCH or SIGALRM interrupting close();
that's just dumb.