Commit 519366f6 authored by Committed by Greg Kroah-HartmanBrowse files
tcp: Prevent low rmem stalls with SO_RCVLOWAT.
[ Upstream commit 435ccfa894e35e3d4a1799e6ac030e48a7b69ef5 ] With SO_RCVLOWAT, under memory pressure, it is possible to enter a state where: 1. We have not received enough bytes to satisfy SO_RCVLOWAT. 2. We have not entered buffer pressure (see tcp_rmem_pressure()). 3. But, we do not have enough buffer space to accept more packets. In this case, we advertise 0 rwnd (due to #3) but the application does not drain the receive queue (no wakeup because of #1 and #2) so the flow stalls. Modify the heuristic for SO_RCVLOWAT so that, if we are advertising rwnd<=rcv_mss, force a wakeup to prevent a stall. Without this patch, setting tcp_rmem to 6143 and disabling TCP autotune causes a stalled flow. With this patch, no stall occurs. This is with RPC-style traffic with large messages. Fixes: 03f45c88 ("tcp: avoid extra wakeups for SO_RCVLOWAT users") Signed-off-by: Arjun Roy <firstname.lastname@example.org> Acked-by: Soheil Hassas Yeganeh <email@example.com> Acked-by: Neal Cardwell <firstname.lastname@example.org> Signed-off-by: Eric Dumazet <email@example.com> Link: https://firstname.lastname@example.org Signed-off-by: Jakub Kicinski <email@example.com> Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org>