https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=11a84cc757ef766505ed037c88c21d87b457862d
commit 11a84cc757ef766505ed037c88c21d87b457862d Author: Johannes Schindelin <[email protected]> AuthorDate: Mon Feb 24 13:22:36 2025 -0800 Commit: Corinna Vinschen <[email protected]> CommitDate: Mon Feb 24 22:33:44 2025 +0100 Cygwin: fix SSH hangs It was reported in https://github.com/git-for-windows/git/issues/5199 that as of v3.5.4, cloning or fetching via SSH is hanging indefinitely. Bisecting the problem points to 555afcb2f3 (Cygwin: select: set pipe writable only if PIPE_BUF bytes left, 2024-08-18). That commit's intention seems to look at the write buffer, and only report the pipe as writable if there are more than one page (4kB) available. However, the number that is looked up is the number of bytes that are already in the buffer, ready to be read, and further analysis shows that in the scenario described in the report, the number of available bytes is substantially below `PIPE_BUF`, but as long as they are not handled, there is apparently a dead-lock. Since the old logic worked, and the new logic causes a dead-lock, let's essentially revert 555afcb2f3a6 ("Cygwin: select: set pipe writable only if PIPE_BUF bytes left"). Note: This is not a straight revert, as the code in question has been modified subsequently, and trying to revert the original commit would cause merge conflicts. Therefore, the diff looks very different from the reverse diff of the commit whose logic is reverted. Fixes: 555afcb2f3a6 ("Cygwin: select: set pipe writable only if PIPE_BUF bytes left") Signed-off-by: Johannes Schindelin <[email protected]> Diff: --- winsup/cygwin/select.cc | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc index 353f074c735a..012578886011 100644 --- a/winsup/cygwin/select.cc +++ b/winsup/cygwin/select.cc @@ -778,7 +778,7 @@ out: } ssize_t n = pipe_data_available (s->fd, fh, h, PDA_SELECT | PDA_WRITE); select_printf ("write: %s, n %d", fh->get_name (), n); - gotone += s->write_ready = (n >= PIPE_BUF); + gotone += s->write_ready = (n > 0); if (n < 0 && s->except_selected) gotone += s->except_ready = true; } @@ -992,7 +992,7 @@ out: ssize_t n = pipe_data_available (s->fd, fh, fh->get_handle (), PDA_SELECT | PDA_WRITE); select_printf ("write: %s, n %d", fh->get_name (), n); - gotone += s->write_ready = (n >= PIPE_BUF); + gotone += s->write_ready = (n > 0); if (n < 0 && s->except_selected) gotone += s->except_ready = true; } @@ -1418,7 +1418,7 @@ out: { ssize_t n = pipe_data_available (s->fd, fh, h, PDA_SELECT | PDA_WRITE); select_printf ("write: %s, n %d", fh->get_name (), n); - gotone += s->write_ready = (n >= PIPE_BUF); + gotone += s->write_ready = (n > 0); if (n < 0 && s->except_selected) gotone += s->except_ready = true; }
