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authorSteven Rostedt (Google) <rostedt@goodmis.org>2024-01-04 16:57:13 -0500
committerSteven Rostedt (Google) <rostedt@goodmis.org>2024-01-04 17:11:58 -0500
commit1e4624eb5a0ecaae0d2c4e3019bece119725bb98 (patch)
treed803c1cf42e1b1bc65e3d85ff582e4703dea5253
parente109deadb73318cf4a3bd61287d969f705df278f (diff)
eventfs: Do ctx->pos update for all iterations in eventfs_iterate()
The ctx->pos was only updated when it added an entry, but the "skip to current pos" check (c--) happened for every loop regardless of if the entry was added or not. This inconsistency caused readdir to be incorrect. It was due to: for (i = 0; i < ei->nr_entries; i++) { if (c > 0) { c--; continue; } mutex_lock(&eventfs_mutex); /* If ei->is_freed then just bail here, nothing more to do */ if (ei->is_freed) { mutex_unlock(&eventfs_mutex); goto out; } r = entry->callback(name, &mode, &cdata, &fops); mutex_unlock(&eventfs_mutex); [..] ctx->pos++; } But this can cause the iterator to return a file that was already read. That's because of the way the callback() works. Some events may not have all files, and the callback can return 0 to tell eventfs to skip the file for this directory. for instance, we have: # ls /sys/kernel/tracing/events/ftrace/function format hist hist_debug id inject and # ls /sys/kernel/tracing/events/sched/sched_switch/ enable filter format hist hist_debug id inject trigger Where the function directory is missing "enable", "filter" and "trigger". That's because the callback() for events has: static int event_callback(const char *name, umode_t *mode, void **data, const struct file_operations **fops) { struct trace_event_file *file = *data; struct trace_event_call *call = file->event_call; [..] /* * Only event directories that can be enabled should have * triggers or filters, with the exception of the "print" * event that can have a "trigger" file. */ if (!(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE)) { if (call->class->reg && strcmp(name, "enable") == 0) { *mode = TRACE_MODE_WRITE; *fops = &ftrace_enable_fops; return 1; } if (strcmp(name, "filter") == 0) { *mode = TRACE_MODE_WRITE; *fops = &ftrace_event_filter_fops; return 1; } } if (!(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE) || strcmp(trace_event_name(call), "print") == 0) { if (strcmp(name, "trigger") == 0) { *mode = TRACE_MODE_WRITE; *fops = &event_trigger_fops; return 1; } } [..] return 0; } Where the function event has the TRACE_EVENT_FL_IGNORE_ENABLE set. This means that the entries array elements for "enable", "filter" and "trigger" when called on the function event will have the callback return 0 and not 1, to tell eventfs to skip these files for it. Because the "skip to current ctx->pos" check happened for all entries, but the ctx->pos++ only happened to entries that exist, it would confuse the reading of a directory. Which would cause: # ls /sys/kernel/tracing/events/ftrace/function/ format hist hist hist_debug hist_debug id inject inject The missing "enable", "filter" and "trigger" caused ls to show "hist", "hist_debug" and "inject" twice. Update the ctx->pos for every iteration to keep its update and the "skip" update consistent. This also means that on error, the ctx->pos needs to be decremented if it was incremented without adding something. Link: https://lore.kernel.org/all/20240104150500.38b15a62@gandalf.local.home/ Link: https://lore.kernel.org/linux-trace-kernel/20240104220048.172295263@goodmis.org Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Fixes: 493ec81a8fb8e ("eventfs: Stop using dcache_readdir() for getdents()") Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
-rw-r--r--fs/tracefs/event_inode.c21
1 files changed, 14 insertions, 7 deletions
diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 0aca6910efb3..c73fb1f7ddbc 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -760,6 +760,8 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
continue;
}
+ ctx->pos++;
+
if (ei_child->is_freed)
continue;
@@ -767,13 +769,12 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
dentry = create_dir_dentry(ei, ei_child, ei_dentry);
if (!dentry)
- goto out;
+ goto out_dec;
ino = dentry->d_inode->i_ino;
dput(dentry);
if (!dir_emit(ctx, name, strlen(name), ino, DT_DIR))
- goto out;
- ctx->pos++;
+ goto out_dec;
}
for (i = 0; i < ei->nr_entries; i++) {
@@ -784,6 +785,8 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
continue;
}
+ ctx->pos++;
+
entry = &ei->entries[i];
name = entry->name;
@@ -791,7 +794,7 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
/* If ei->is_freed then just bail here, nothing more to do */
if (ei->is_freed) {
mutex_unlock(&eventfs_mutex);
- goto out;
+ goto out_dec;
}
r = entry->callback(name, &mode, &cdata, &fops);
mutex_unlock(&eventfs_mutex);
@@ -800,19 +803,23 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
dentry = create_file_dentry(ei, i, ei_dentry, name, mode, cdata, fops);
if (!dentry)
- goto out;
+ goto out_dec;
ino = dentry->d_inode->i_ino;
dput(dentry);
if (!dir_emit(ctx, name, strlen(name), ino, DT_REG))
- goto out;
- ctx->pos++;
+ goto out_dec;
}
ret = 1;
out:
srcu_read_unlock(&eventfs_srcu, idx);
return ret;
+
+ out_dec:
+ /* Incremented ctx->pos without adding something, reset it */
+ ctx->pos--;
+ goto out;
}
/**