diff options
Diffstat (limited to 'src/runtime')
| -rw-r--r-- | src/runtime/proc.go | 29 |
1 files changed, 25 insertions, 4 deletions
diff --git a/src/runtime/proc.go b/src/runtime/proc.go index 0c5089d4f0..db4eb21cb8 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -779,7 +779,16 @@ func dumpgstatus(gp *g) { func checkmcount() { assertLockHeld(&sched.lock) - if mcount() > sched.maxmcount { + // Exclude extra M's, which are used for cgocallback from threads + // created in C. + // + // The purpose of the SetMaxThreads limit is to avoid accidental fork + // bomb from something like millions of goroutines blocking on system + // calls, causing the runtime to create millions of threads. By + // definition, this isn't a problem for threads created in C, so we + // exclude them from the limit. See https://go.dev/issue/60004. + count := mcount() - int32(extraMInUse.Load()) - int32(extraMLength.Load()) + if count > sched.maxmcount { print("runtime: program exceeds ", sched.maxmcount, "-thread limit\n") throw("thread exhaustion") } @@ -2015,7 +2024,7 @@ func oneNewExtraM() { sched.ngsys.Add(1) // Add m to the extra list. - putExtraM(mp) + addExtraM(mp) } // dropm is called when a cgo callback has called needm but is now @@ -2084,6 +2093,9 @@ var ( extraMLength atomic.Uint32 // Number of waiters in lockextra. extraMWaiters atomic.Uint32 + + // Number of extra M's in use by threads. + extraMInUse atomic.Uint32 ) // lockextra locks the extra list and returns the list head. @@ -2115,6 +2127,7 @@ func lockextra(nilokay bool) *m { continue } if extraM.CompareAndSwap(old, locked) { + extraMInUse.Add(1) return (*m)(unsafe.Pointer(old)) } osyield_no_g() @@ -2128,7 +2141,6 @@ func unlockextra(mp *m, delta int32) { extraM.Store(uintptr(unsafe.Pointer(mp))) } - // Return an M from the extra M list. Returns last == true if the list becomes // empty because of this call. // @@ -2143,10 +2155,19 @@ func getExtraM(nilokay bool) (mp *m, last bool) { return mp, mp.schedlink.ptr() == nil } -// Put an extra M on the list. +// Returns an extra M back to the list. mp must be from getExtraM. Newly +// allocated M's should use addExtraM. // //go:nosplit func putExtraM(mp *m) { + extraMInUse.Add(-1) + addExtraM(mp) +} + +// Adds a newly allocated M to the extra M list. +// +//go:nosplit +func addExtraM(mp *m) { mnext := lockextra(true) mp.schedlink.set(mnext) unlockextra(mp, 1) |