random: simplify accounting code (0fb7a01a) · Commits · 戴 / test

With this we handle "reserved" in just one place. As a bonus the code becomes less nested, and the "wakeup_write" flag variable becomes unnecessary. The variable "flags" was already unused. This code behaves identically to the previous version except in two pathological cases that don't occur. If the argument "nbytes" is already less than "min", then we didn't previously enforce "min". If r->limit is false while "reserved" is nonzero, then we previously applied "reserved" in checking whether we had enough bits, even though we don't apply it to actually limit how many we take. The callers of account() never exercise either of these cases. Before the previous commit, it was possible for "nbytes" to be less than "min" if userspace chose a pathological configuration, but no longer. Cc: Jiri Kosina <jkosina@suse.cz> Cc: "H. Peter Anvin" <hpa@zytor.com> Signed-off-by:

Greg Price <price@mit.edu> Signed-off-by:

"Theodore Ts'o" <tytso@mit.edu>

drivers/char/random.c

+10 −17

Original line number	Diff line number	Diff line
		@@ -964,8 +964,6 @@ static void push_to_pool(struct work_struct *work)
		static size_t account(struct entropy_store *r, size_t nbytes, int min,
		int reserved)
		{
		unsigned long flags;
		int wakeup_write = 0;
		int have_bytes;
		int entropy_count, orig;
		size_t ibytes;
		@@ -977,24 +975,19 @@ retry:
		entropy_count = orig = ACCESS_ONCE(r->entropy_count);
		have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
		ibytes = nbytes;
		if (have_bytes < min + reserved) {
		ibytes = 0;
		} else {
		/* If limited, never pull more than available */
		if (r->limit)
		ibytes = min_t(size_t, ibytes, have_bytes - reserved);
		if (ibytes < min)
		ibytes = 0;
		entropy_count = max_t(int, 0,
		entropy_count - (ibytes << (ENTROPY_SHIFT + 3)));
		if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
		goto retry;

		if ((r->entropy_count >> ENTROPY_SHIFT)
		< random_write_wakeup_thresh)
		wakeup_write = 1;
		}

		trace_debit_entropy(r->name, 8 * ibytes);
		if (wakeup_write) {
		if (ibytes &&
		(r->entropy_count >> ENTROPY_SHIFT) < random_write_wakeup_thresh) {
		wake_up_interruptible(&random_write_wait);
		kill_fasync(&fasync, SIGIO, POLL_OUT);
		}

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