From: Andrew Morton Date: Wed, 4 Feb 2009 23:12:06 +0000 (-0800) Subject: revert "rlimit: permit setting RLIMIT_NOFILE to RLIM_INFINITY" X-Git-Tag: firefly_0821_release~15647 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=60fd760fb9ff7034360bab7137c917c0330628c2;p=firefly-linux-kernel-4.4.55.git revert "rlimit: permit setting RLIMIT_NOFILE to RLIM_INFINITY" Revert commit 0c2d64fb6cae9aae480f6a46cfe79f8d7d48b59f because it causes (arguably poorly designed) existing userspace to spend interminable periods closing billions of not-open file descriptors. We could bring this back, with some sort of opt-in tunable in /proc, which defaults to "off". Peter's alanysis follows: : I spent several hours trying to get to the bottom of a serious : performance issue that appeared on one of our servers after upgrading to : 2.6.28. In the end it's what could be considered a userspace bug that : was triggered by a change in 2.6.28. Since this might also affect other : people I figured I'd at least document what I found here, and maybe we : can even do something about it: : : : So, I upgraded some of debian.org's machines to 2.6.28.1 and immediately : the team maintaining our ftp archive complained that one of their : scripts that previously ran in a few minutes still hadn't even come : close to being done after an hour or so. Downgrading to 2.6.27 fixed : that. : : Turns out that script is forking a lot and something in it or python or : whereever closes all the file descriptors it doesn't want to pass on. : That is, it starts at zero and goes up to ulimit -n/RLIMIT_NOFILE and : closes them all with a few exceptions. : : Turns out that takes a long time when your limit -n is now 2^20 (1048576). : : With 2.6.27.* the ulimit -n was the standard 1024, but with 2.6.28 it is : now a thousand times that. : : 2.6.28 included a patch titled "rlimit: permit setting RLIMIT_NOFILE to : RLIM_INFINITY" (0c2d64fb6cae9aae480f6a46cfe79f8d7d48b59f)[1] that : allows, as the title implies, to set the limit for number of files to : infinity. : : Closer investigation showed that the broken default ulimit did not apply : to "system" processes (like stuff started from init). In the end I : could establish that all processes that passed through pam_limit at one : point had the bad resource limit. : : Apparently the pam library in Debian etch (4.0) initializes the limits : to some default values when it doesn't have any settings in limit.conf : to override them. Turns out that for nofiles this is RLIM_INFINITY. : Commenting out "case RLIMIT_NOFILE" in pam_limit.c:267 of our pam : package version 0.79-5 fixes that - tho I'm not sure what side effects : that has. : : Debian lenny (the upcoming 5.0 version) doesn't have this issue as it : uses a different pam (version). Reported-by: Peter Palfrader Cc: Adam Tkac Cc: Michael Kerrisk Cc: [2.6.28.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/sys.c b/kernel/sys.c index e7dc0e10a485..f145c415bc16 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1525,22 +1525,14 @@ SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim) return -EINVAL; if (copy_from_user(&new_rlim, rlim, sizeof(*rlim))) return -EFAULT; + if (new_rlim.rlim_cur > new_rlim.rlim_max) + return -EINVAL; old_rlim = current->signal->rlim + resource; if ((new_rlim.rlim_max > old_rlim->rlim_max) && !capable(CAP_SYS_RESOURCE)) return -EPERM; - - if (resource == RLIMIT_NOFILE) { - if (new_rlim.rlim_max == RLIM_INFINITY) - new_rlim.rlim_max = sysctl_nr_open; - if (new_rlim.rlim_cur == RLIM_INFINITY) - new_rlim.rlim_cur = sysctl_nr_open; - if (new_rlim.rlim_max > sysctl_nr_open) - return -EPERM; - } - - if (new_rlim.rlim_cur > new_rlim.rlim_max) - return -EINVAL; + if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > sysctl_nr_open) + return -EPERM; retval = security_task_setrlimit(resource, &new_rlim); if (retval)