af_unix: Remove lock dance in unix_peek_fds().

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In the previous GC implementation, the shape of the inflight socket
graph was not expected to change while GC was in progress.

MSG_PEEK was tricky because it could install inflight fd silently
and transform the graph.

Let's say we peeked a fd, which was a listening socket, and accept()ed
some embryo sockets from it.  The garbage collection algorithm would
have been confused because the set of sockets visited in scan_inflight()
would change within the same GC invocation.

That's why we placed spin_lock(&unix_gc_lock) and spin_unlock() in
unix_peek_fds() with a fat comment.

In the new GC implementation, we no longer garbage-collect the socket
if it exists in another queue, that is, if it has a bridge to another
SCC.  Also, accept() will require the lock if it has edges.

Thus, we need not do the complicated lock dance.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240401173125.92184-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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This commit is contained in:

Kuniyuki Iwashima 2024-04-01 10:31:25 -07:00 • committed by Jakub Kicinski

parent 7c349ed090

commit 118f457da9

3 changed files with 1 additions and 44 deletions

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1

include/net/af_unix.h

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42

net/unix/af_unix.c

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2

net/unix/garbage.c

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