Author: cem Date: Fri Mar 16 18:50:26 2018 New Revision: 331070 URL: https://svnweb.freebsd.org/changeset/base/331070
Log: random(4): Poll for signals during large reads Occasionally poll for signals during large reads of the /dev/u?random devices. This allows cancellation via SIGINT of accidental invocations of very large reads. (A 2GB /dev/random read, which takes about 10 seconds on my 2017 AMD Zen processor, can be aborted.) I believe this behavior was intended since 2014 (r273997), just not fully implemented. This is motivated by a potential getrandom(2) interface that may not explicitly forbid extremely large reads on 64-bit platforms -- even larger than the 2GB limit imposed on devfs I/O by default. Such reads, if they are to be allowed, should be cancellable by the user or administrator. Reviewed by: delphij Approved by: secteam (delphij) Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D14684 Modified: head/sys/dev/random/randomdev.c Modified: head/sys/dev/random/randomdev.c ============================================================================== --- head/sys/dev/random/randomdev.c Fri Mar 16 18:16:31 2018 (r331069) +++ head/sys/dev/random/randomdev.c Fri Mar 16 18:50:26 2018 (r331070) @@ -130,7 +130,13 @@ READ_RANDOM_UIO(struct uio *uio, bool nonblock) uint8_t *random_buf; int error, spamcount; ssize_t read_len, total_read, c; + /* 16 MiB takes about 0.08 s CPU time on my 2017 AMD Zen CPU */ +#define SIGCHK_PERIOD (16 * 1024 * 1024) + const size_t sigchk_period = SIGCHK_PERIOD; + CTASSERT(SIGCHK_PERIOD % PAGE_SIZE == 0); +#undef SIGCHK_PERIOD + random_buf = malloc(PAGE_SIZE, M_ENTROPY, M_WAITOK); p_random_alg_context->ra_pre_read(); error = 0; @@ -167,11 +173,22 @@ READ_RANDOM_UIO(struct uio *uio, bool nonblock) read_len = MIN(read_len, PAGE_SIZE); p_random_alg_context->ra_read(random_buf, read_len); c = MIN(uio->uio_resid, read_len); + /* + * uiomove() may yield the CPU before each 'c' bytes + * (up to PAGE_SIZE) are copied out. + */ error = uiomove(random_buf, c, uio); total_read += c; + /* + * Poll for signals every few MBs to avoid very long + * uninterruptible syscalls. + */ + if (error == 0 && uio->uio_resid != 0 && + total_read % sigchk_period == 0) + error = tsleep_sbt(&random_alg_context, PCATCH, + "randrd", SBT_1NS, 0, C_HARDCLOCK); } - if (total_read != uio->uio_resid && (error == ERESTART || error == EINTR)) - /* Return partial read, not error. */ + if (error == ERESTART || error == EINTR) error = 0; } free(random_buf, M_ENTROPY); _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
