Subject: [merged] random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update.patch removed from -mm tree To: jkosina@xxxxxxx,greg@xxxxxxxxx,stable@xxxxxxxxxxxxxxx,tytso@xxxxxxx,mm-commits@xxxxxxxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Tue, 28 May 2013 12:37:19 -0700 The patch titled Subject: random: fix accounting race condition with lockless irq entropy_count update has been removed from the -mm tree. Its filename was random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Jiri Kosina <jkosina@xxxxxxx> Subject: random: fix accounting race condition with lockless irq entropy_count update Commit 902c098a3663 ("random: use lockless techniques in the interrupt path") turned IRQ path from being spinlock protected into lockless cmpxchg-retry update. That commit removed r->lock serialization between crediting entropy bits from IRQ context and accounting when extracting entropy on userspace read path, but didn't turn the r->entropy_count reads/updates in account() to use cmpxchg as well. It has been observed, that under certain circumstances this leads to read() on /dev/urandom to return 0 (EOF), as r->entropy_count gets corrupted and becomes negative, which in turn results in propagating 0 all the way from account() to the actual read() call. Convert the accounting code to be the proper lockless counterpart of what has been partially done by 902c098a3663. Signed-off-by: Jiri Kosina <jkosina@xxxxxxx> Cc: Theodore Ts'o <tytso@xxxxxxx> Cc: Greg KH <greg@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/char/random.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff -puN drivers/char/random.c~random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update drivers/char/random.c --- a/drivers/char/random.c~random-fix-accounting-race-condition-with-lockless-irq-entropy_count-update +++ a/drivers/char/random.c @@ -865,16 +865,24 @@ static size_t account(struct entropy_sto if (r->entropy_count / 8 < min + reserved) { nbytes = 0; } else { + int entropy_count, orig; +retry: + entropy_count = orig = ACCESS_ONCE(r->entropy_count); /* If limited, never pull more than available */ - if (r->limit && nbytes + reserved >= r->entropy_count / 8) - nbytes = r->entropy_count/8 - reserved; + if (r->limit && nbytes + reserved >= entropy_count / 8) + nbytes = entropy_count/8 - reserved; - if (r->entropy_count / 8 >= nbytes + reserved) - r->entropy_count -= nbytes*8; - else - r->entropy_count = reserved; + if (entropy_count / 8 >= nbytes + reserved) { + entropy_count -= nbytes*8; + if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) + goto retry; + } else { + entropy_count = reserved; + if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) + goto retry; + } - if (r->entropy_count < random_write_wakeup_thresh) + if (entropy_count < random_write_wakeup_thresh) wakeup_write = 1; } _ Patches currently in -mm which might be from jkosina@xxxxxxx are linux-next.patch lib-bitmapc-speed-up-bitmap_find_free_region.patch lib-bitmapc-speed-up-bitmap_find_free_region-fix.patch rtc-rtc-hid-sensor-time-allow-full-years-16bit-in-hid-reports.patch rtc-rtc-hid-sensor-time-allow-16-and-32-bit-values-for-all-attributes.patch rtc-rtc-hid-sensor-time-add-option-hctosys-to-set-time-at-boot.patch rtc-rtc-hid-sensor-time-add-support-for-milliseconds.patch mwave-fix-info-leak-in-mwave_ioctl.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html