Date: Mon, 29 Jun 2020 21:35:50 +0000 (UTC) From: Andrew Gallatin <gallatin@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r362789 - head/sys/kern Message-ID: <202006292135.05TLZo2d034398@repo.freebsd.org>
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Author: gallatin Date: Mon Jun 29 21:35:50 2020 New Revision: 362789 URL: https://svnweb.freebsd.org/changeset/base/362789 Log: Fix a panic when unloading firmware LIST_FOREACH_SAFE() is not safe in the presence of other threads removing list entries when a mutex is released. This is not in the critical path, so just restart the scan each time we drop the lock, rather than using a marker. Reviewed by: jhb, markj Sponsored by: Netflix Modified: head/sys/kern/subr_firmware.c Modified: head/sys/kern/subr_firmware.c ============================================================================== --- head/sys/kern/subr_firmware.c Mon Jun 29 19:30:35 2020 (r362788) +++ head/sys/kern/subr_firmware.c Mon Jun 29 21:35:50 2020 (r362789) @@ -394,14 +394,12 @@ EVENTHANDLER_DEFINE(mountroot, firmware_mountroot, NUL static void unloadentry(void *unused1, int unused2) { - struct priv_fw *fp, *tmp; + struct priv_fw *fp; int err; - bool changed; mtx_lock(&firmware_mtx); - changed = false; restart: - LIST_FOREACH_SAFE(fp, &firmware_table, link, tmp) { + LIST_FOREACH(fp, &firmware_table, link) { if (fp->file == NULL || fp->refcnt != 0 || (fp->flags & FW_UNLOAD) == 0) continue; @@ -412,7 +410,6 @@ restart: * 2. clear FW_UNLOAD so we don't try this entry again. * 3. release the lock while trying to unload the module. */ - changed = true; fp->flags &= ~FW_UNLOAD; /* do not try again */ /* @@ -422,9 +419,11 @@ restart: mtx_unlock(&firmware_mtx); err = linker_release_module(NULL, NULL, fp->file); mtx_lock(&firmware_mtx); - } - if (changed) { - changed = false; + + /* + * When we dropped the lock, another thread could have + * removed an element, so we must restart the scan. + */ goto restart; } mtx_unlock(&firmware_mtx);
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