This patch exists in the git-for-windows fork of msys2-runtime (which is itself a fork of cygwin). There have been complaints and requests to apply this patch to msys2-runtime (such as https://github.com/msys2/MSYS2-packages/issues/4962), but it makes more sense to me to try to figure this out upstream, so everyone can benefit. I did not write the patch, nor do I personally encounter the bug it is intended to fix, so I can't really advocate for its approach, but the commit message is pretty detailed as to the investigation that led to it.
This is the original patch from https://github.com/git-for-windows/msys2-runtime/pull/75, if necessary I can rebase it on cygwin's master branch, it does so cleanly (or you can try git am -3, that tends to work for me in cases where straight git am does not). -- >8 -- >From cbe555e054cefeccd65250bb11dc56f82196301f Mon Sep 17 00:00:00 2001 From: Johannes Schindelin <johannes.schinde...@gmx.de> Date: Thu, 10 Oct 2024 19:52:47 +0200 Subject: [PATCH] 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 555afcb2f3 (Cygwin: select: set pipe writable only if PIPE_BUF bytes left, 2024-08-18). 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. Signed-off-by: Johannes Schindelin <johannes.schinde...@gmx.de> --- 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 bc02c3f9d4..2c09b14d1c 100644 --- a/winsup/cygwin/select.cc +++ b/winsup/cygwin/select.cc @@ -776,7 +776,7 @@ peek_pipe (select_record *s, bool from_select) } 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; } @@ -990,7 +990,7 @@ peek_fifo (select_record *s, bool from_select) 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; } @@ -1416,7 +1416,7 @@ peek_pty_slave (select_record *s, bool from_select) { 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; }
